methods for detecting and identifying carcinogens

4Methods for Detecting and

Identifying Carcinogens

Contents

PageMethods . . . . . . . . .......................113

Analysis of Molecular Structure and OtherPhysical Constants, . ..................114

Short-Term Tests . . . . . . . . . . . . . . . . . . . . . . . .115The Ames Test. . . ......................116Other Short-TermTests. . ................120Use of Short-TermTestResults andPolicy

Statements About the Tests . ......,.....121

Bioassays . . . . . . . . . . . . . . . . . . . . . . . . .. ....122Standard Protocols for Bioassays. . .........123Objections to the Usefulness of Bioassays ....124Expert Review of Bioassay Results . .........127Policy Considerations About Bioassays. ... ..l28How Many Chemicals Are Carcinogens in

Animal Tests? . . . . . . . . . . . . . . . . . . . . . . .129

Selection of Chemicals forTesting in Bioassaysand Short-Term Tests . . . . . . . . . . . . . . . ..131

The Interagency Testing Committee . .......131National Toxicology Program . ............133The National Center for Toxicological

R e s e a r c h . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 4Chemical Industry Institute of Toxicology. ...l35

Tier Testing. . . . . . . . . . . . . . . . . . . ... .;. ....135

Epidemiology . . . . . . . . . . . . . . . . . . . . . . . . .136Descriptive Epidemiology . ...............137Observational Epidemiology. . ............137Causal Associations. . ...................138Policy Considerations About Epidemiology. ..l38Carcinogens for Which There is Human

E v i d e n c e . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 4 6Annual Report on Carcinogens . ...........140

Sources of Epidemiologically Useful Data ... ...l42Health Status Information. . ..............142Exposure Data. . . . . . . . . . . . . . . . . ... ... ..145Chemical Information Systems . ...........146Collection and Coordination of Exposure

and Health Data. . . . . . . . . . . . . . . . . . . . . .149Government Records and Record Linkage. ...l5l

S u m m a r y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 2

LIST OF TABLES

Table No. Page23. General Classification of Tests Available

24.

25.

26.

27.28.

29.

30.

31.

To Determine Properties Related toCarcinogenicity. . . . ...................114Results Obtained in Two Validation Studiesof the Ames Test WhenKnownCarcinogens and Noncarcinogens WereTested . . . . . . . . . . ....................118Expected Results of Examining TwoCollections of Chemicals for MutagenicityUsing a Short-Term Test That is 90-PercentSensitive and 90-Percent Specific: OneCollection of Chemicals Contains 1 PercentCarcinogens; the Other Contains 10Percent .119Distribution and Number of Animals in aTypical Bioassay Study of Carcinogens. ....124Guidelines for Bioassay in SmalI Rodents ...125Some Organizations That Have Consideredand Endorsed Animal Tests as Predictors ofHuman Risk From Chemical Carcinogens ...l29Advantages and Disadvantages of Case-Control and Cohort Studies .. ... ... :. ...139Chemicals and Industrial ProcessesEvaluated for Human Carcinogenicity bythe International Agency for Researchon Cancer. . . . . . . . . . . . . . . . . . . . . . . . . . .141EPA’s Recommended Base Set of Data ToBe Included in Premanufacturing Notices ...148

LIST OF FIGURES

Figure No. Page19. Molecular Structures of Two Closely

Related Chemicals: One a Carcinogen andOne a Noncarcinogen . .................115

20. 1nterrelationships of Major TestingActivities of NTP . ....................136

4.Methods for Detecting and

Identifying Carcinogens

Beginning with this chapter, the focus of thisreport shifts from all causes of cancer to onlychemicals. This shift does not represent a deci-sion that chemicals, in the workplace or in thegeneral environment, are more important incancer causation than dietary elements, per-sonal habits, radiation, or certain aspects ofhuman biology. However, it does reflect the ma-jor legislative and regulatory emphasis recentlyplaced on chemicals, and the greater ease with

METHODS

There are four major methods for detectingand identifying carcinogens:

1.2.3.

4.

molecular structure analysis,short-term tests,long-term chronic bioassays in laboratoryanimals (termed “bioassays” or “animaltests” hereafter), andepidemiology.

The first two methods produce informationabout potential carcinogenicity; the third pro-vides direct evidence of carcinogenicity inanimals; the fourth produces direct evidenceabout cancer in man. These categories are brief-ly described in table 23.

Probably no statement made in the last col-umn of table 23 is free from dispute. Resultsmay be, and frequently are, challenged for sev-eral reasons: because the test was incorrectly de-signed or executed (all methods); because themethod does not directly measure carcinogenici-ty (methods 1 and 2); because the test is toosensitive and produces false positives (methods2 and 3); because the test is too insensitive andproduces false negatives (method 4); and be-cause the test does not measure human experi-ence (all methods but 4), etc.

which chemical carcinogens can be detected bypresent-day methods.

Different methods are available, employingdifferent techniques, using different test orga-nisms, and producing different types of infor-mation about carcinogenicity. This chapterdiscusses a variety of those methods, theirstrengths and weaknesses, some results fromeach, and the tools they require.

Knowledge about tests and about the validityof test results increases as the tests are moreoften used, more discussed, and more refined.The state of scientific knowledge plays an im-portant role in decisions to test or not to test achemical, decisions about which tests are appro-priate, and decisions about interpretation of thetest results. As will be discussed, “policy state-merits, ” sometimes issued as guidelines or stand-ards, detail the methods that an organizationwill use in making decisions. A certain tension isapparent in all the policies. Tests cost moneyand take time; bigger and better tests cost moreand take more time; compromises are necessaryin the design of each test so that a reasonablenumber of chemicals can be tested.

An equally important issue is the amount ofinformation necessary to decide that a chemicalis or is not a carcinogen that requires some con-trol action. The fact that some regulations arebased on nonhuman test systems shows thatproof that a chemical is a human carcinogen isnot demanded. This illustrates that preventionof cancer is seen as so important that it is ap-propriate to make decisions to restrict exposuresbefore human damage is observed.

113

114 ● Technologies for Determining Cancer Risks From the Environment

Table 23.—General Classification of Tests Available To Determine Properties Related to Carcinogenicity

Time Conclusion, if resultMethod System required Basis for test Result is positive

Molecular “Paper chem- Daysstructure istry”analysis

Basic labor- Weeksatory tests

Short-term Bacteria, yeast, Generallytests cultured cells, few weeks

intact animals (range 1 dayto 8 months)

Bioassay Intact animals(rats, mice)

2 to 5 years

Epidemiology Humans Months tolifetimes

Chemicals withlike structuresinteract similarlywith DNA

Chemical inter-action with DNAcan be measuredin biologicalsystems

Chemicals thatcause tumors inanimals maycause tumors inhumans

Chemicals thatcause cancercan be detectedin studies ofhumanpopulations

Structure resembles(positive) or does notresemble (negative)structure of knowncarcinogen

Chemical causes(positive) or does notcause (negative) a re-sponse known to becaused by carcinogens

Chemical causes (posi-tive) or does not cause(negative) increased in-cidence of tumors

Chemical is associated(positive) or is not asso-ciated (negative) withan increased incidenceof cancer

Chemical may behazardous. That deter-mination requiresfurther testing.

Chemical is a poten-tial carcinogen.

Chemical is recognizedas a carcinogen in thatspecies and as a poten-tial human carcinogen.

Chemical is recognizedas a human carcinogen.

SOURCE Office of Technology Assessment

ANALYSIS OF MOLECULAR STRUCTURE ANDOTHER PHYSICAL CONSTANTS

Some information about the likelihood of achemical being a carcinogen maybe obtained bycomparing its structure and chemical and physi-cal characteristics with those of known carcino-gens and noncarcinogens. This first stage in anorderly determination of whether or not a chem-ical is a carcinogen requires the gathering of allavailable information about it. The informationcan be obtained from sources as diverse as re-sults from testing a chemical in animals to anec-dotal stories about human disease, but the mostreadily available information is often about themolecular structure and physical and chemicalproperties of the suspect chemical.

Certain molecular structures have been asso-ciated with carcinogenicity, and structural simi-larity is used in making decisions about whichagents are more or less suspect. For instance, 8of the first 14 carcinogens regulated by theOccupational Safety and Health Administration(OSHA) are aromatic amines. The Environ-mental Protection Agency (EPA) relies heavily

on structural analysis in determining whether ornot “new” chemicals, described in premanu-facturing notices, may present an unreasonablerisk to health or the environment. Chemical andphysical properties which are useful in evaluat-ing a chemical’s carcinogenic potential includevolubility, stability, sensitivity to pH, andchemical reactivity. Often this type of informa-tion is generated by the manufacturer of thechemical.

A number of proposals have been made thatchemicals be divided up into classes dependingon their structural similarities and that testingbe done on a number of members in each class.Unfortunately, carcinogens are known in sever-al chemical classes, and “ . . . the dozen ormore known classes of these agents [carcino-gens] share no common structural features”(239). Furthermore, even within classes, closely

related chemicals may differ with respect to car-cinogenicity—e.g., 2-acetylaminofluorene (2-AAF) is a well-documented carcinogen; its

Ch. 4—Metkods for Detecting and ldentifying Carcinogens ● 115

chemical relative, 4-acetylaminofluorene (4-AAF), is not a carcinogen (see figure 19).

Figure 19.— Molecular Structures of Two CloselyRelated Chemicals: One a Carcinogen and

One a Noncarcinogen

2-acetylamlnofluorene, a known carcinogen

4-acetylaminofluorene, a noncarcinogen

SOURCE. Off Ice of Technology Assessment

EPA recently based a regulatory decision onmolecular structural analysis. Under section 5(e)of the Toxic Substances Control Act (TSCA),EPA prohibited the entry of six new chemicalsubstances into the marketplace unless themanufacturer provided additional informationabout toxicity. A National Cancer Institute(NCI) bioassay had shown a related chemical tobe carcinogenic, and based on that result, EPAdecided that more information was needed be-fore manufacture could begin (88). The manu-facturer decided not to proceed with the testingand did not market the chemicals.

Short-term tests are so named because of therelatively short time needed to conduct the ex-periments. Some studies involving micro-orga-nisms require less than 1 day to complete (87),most require a few days to a few weeks, and thelongest, using mice, requires 8 to 9 months(172), These times may be compared to themore than 3 years required to complete a bio-assay and the months to years required to com-plete epidemiologic studies.

A number of reasons account for the growinginterest in using short-term tests to predict achemical’s carcinogenic potential:

● shorter time period required for the tests;

● low cost ($100 to a few thousand dollars foreach test compared to $400,000 to $1 mil-lion for a bioassay);

● evidence that the majority of chemical car-cinogens are mutagens and that many mu-tagens are carcinogens;

● growing opinion that short-term testscan predict which chemicals may be car-cinogens.

The third point is important because manyshort-term tests determine whether or not achemical causes mutations (mutagenicity) ratherthan if it causes cancer (carcinogenicity). Thepostulated relationship between mutagenicityand carcinogenicity stems from biological prop-erties common to all living organisms. Thegenetic information in both germ cells (egg andsperm) and somatic cells (nongerm or “bodycells”) is composed of deoxyribonucleic acid(DNA), and agents that cause mutations in germcells are also expected to cause mutations insomatic cells. A germ cell mutation may prevent


the formation of viable offspring, cause a ge-netic malformation, or produce subtle defects inthe progeny, such as minimal depression in in-telligence or increased susceptibility to disease.

The consequences of somatic cell mutationsare quite different from those in germ cells.Somatic cells do not contribute genetic informa-tion to succeeding generations, but as each so-matic cell grows and divides, copies of its DNAare passed on to its two “daughter” cells. Somesomatic cell mutations result in uncontrolledcellular growth: The normal tightly controlledgrowth pattern of the somatic cell is brokendown, the cell grows and divides more quicklythan it should, progeny cells exhibit the sameuncontrolled growth, and cancer results.

The hypothesis that assigns genetic changes insomatic cells a role in cancer initiation is re-ferred to as “the somatic mutation theory ofcancer.” Cairns (42) discusses the origin anddevelopment of this theory, which provides in-tellectual support for associating mutagenicityand related changes measured in short-termtests with potential carcinogenicity.

The short-term tests that depend on muta-genicity can detect only materials that interactwith DNA. Some cancers may be caused byother, “epigenetic,” pathways that may not in-volve alterations in genetic information (317).Short-term tests cannot detect such activities.Additionally, short-term tests do not detect pro-moters that do not interact with DNA. The gen-erally good correlation between mutagenic andcarcinogenic activity as well as the bulk ofresults from basic cancer biological researchsupport the notion that carcinogens generallyinteract with DNA.

The Ames Test

The most widely used and best-studied short-term test, the “Ames test, ” is named for itsdeveloper, Bruce Ames, a molecular biologist.The test measures the capacity of a chemical tocause mutations in the bacterium Salmonellatyphimurium, a favorite tool for laboratory in-vestigations since the 1940’s. Salmonella’sgenetics and biochemistry are well understood:it is quickly and easily grown; it presents few

manipulative problems in the laboratory, andtest results are easily interpretable and repro-ducible between laboratories.

Basically, the Ames test involves mixing thechemical under test with a bacterial culture andthen manipulating the culture so that only mu-tated bacteria will grow. The number of mu-tated bacteria is a measure of the potency of thetested material as a mutagen.

It is well known that some chemicals must bealtered before they interact with DNA and thatin humans and other mammals these changesare often accomplished by enzymes in the liver.The addition of liver extracts to the Ames testsystem and to other short-term tests providesa mechanism for these metabolic activationchanges to be accomplished. Generally, extractsare prepared from rats, hamsters, or other lab-oratory animals. The source of the extracts andthe amount used in the tests affect results, andcareful experiments report these specifics so thatothers can replicate the tests. Some chemicalsare “activated” by bacteria normally present inthe intestine rather than by the liver. Theaddition of extracts of such bacteria to Amestest mixtures has been shown to activate somechemicals to mutagenic forms (338).

As of early 1979, more than 2,600 Ames testresults had been published (172). The interestedreader is referred to Hollstein et al. (172) andDevoret (87) for more detailed descriptions ofthe tests, to Ames (11) for a description of theproblems of carcinogen identification addressedby short-term tests, to a series of papers in theApril 1979 issue of the Journal of the NationalCancer Institute and to Bartsch et al. (22) aboutexperiments to validate the reliability of short-term tests.

Short-term tests are still in their infancy; de-velopment of the Ames test began about 15years ago (11). The major factor influencing theacceptance or rejection of any short-term test asa method for identifying carcinogens is a dem-onstration that the test can discriminate be-tween carcinogens and noncarcinogens.

The crux of validation experiments is deter-mining: 1) how frequently carcinogens are cor-rectly identified by short-term tests (sensitivity)

Ch. 4—Methods for Detecting and ldentifying Carcinogens ● 117

and 2) how frequently noncarcinogens are cor-rectly identified (specificity). Ideally the fre-quency for both sensitivity and specificitywould be 100 percent. If the Ames test workedperfectly, every tested carcinogen would be amutagen; every tested noncarcinogen would bea nonmutagen in the test.

The difference between the ideal and themeasured performance can be expressed interms of sensitivity. If the test identified 90 of100 carcinogens as mutagens, it would have asensitivity of 90 percent. The same observationcan be described in terms of its false-negativerate. In the example, 10 carcinogens were falselynegative in the mutagenicity test, so it had a 10-percent false-negative rate.

Similarly for noncarcinogens, the test’s suc-cess can be expressed as a specificity rate. If itidentified 90 of 100 noncarcinogens as nonmuta-gens, its specificity was 90 percent. Alternative-ly, the result can be expressed in terms of thefalse-positive rate, which is 10 percent in theexample.

Ames and his associates tested agents that hadbeen classified as carcinogens or noncarcinogensin bioassays. They found that 156 of 174 animalcarcinogens (90 percent) were mutagenic, and,equally important, 96 of 108 (88 percent) chem-icals classified as noncarcinogens were not mu-tagenic (227). Ames has suggested that some ofthe “noncarcinogenic” chemicals that weredetected as mutagens might have been incorrect-ly classified as noncarcinogens on the basis ofbioassay results (11,227). His suggestion pointsup a problem inherent in “validating” any testagainst the results of other tests: There is noguarantee that the results of the tests that areused as standards are completely accurate.

Other researchers have investigated the cor-relation between Ames test mutagenicity andanimal carcinogenicity in efforts to validate themutagenicity test for predicting carcinogenicity.The good correlation between mutagenicity andcarcinogenicity found by McCann et al. (227)was “confirmed in a smaller . . . study by theImperial Chemical Industries” (34). (In addition,see for instance 13,22,226,309,335). There isgeneral agreement that the tests are predictive,

but some disagreement about whether they are70-, 80-, or 90-percent sensitive. A number offactors contribute to the observed differences insensitivity. For instance, better correlations mayreflect testing chemical classes on which theAmes test performs well. Ames has shown thathis test does not work well with certain classesof chemicals, e.g., halogenated hydrocarbonsand metals, and including those in validationtests decreases the sensitivity of the tests.

Bartsch et al. (22) report on 89 chemicalsstudied in the Ames test for mutagenicity. The89 were chosen because sufficient data existed toclassify each of them as a carcinogen or non-carcinogen in animal tests. Results from theBartsch et al. (22) study along with those froman earlier study by McCann et al. (227) areshown in table 24.

It can be seen that 76 percent of the tested car-cinogens were mutagenic in the Bartsch experi-ments as compared to the 90 percent that werereported mutagenic in McCann et al. (227). Thesensitivity in the former study was lower, butcomparable to the other report, The comparisonof specificity is somewhat deceiving. The 57-percent specificity recorded by Bartsch et al.(22) is much lower than the 88 percent from theearlier study, but results from only seven non-carcinogens were reported by Bartsch et al. (22).McCann et al. (237) tested 108 noncarcinogens.The 57 percent is subject to much larger errorthan the higher estimate of specificity.

In both reports, the predictive value wasfound to be over 90 percent. The predictive val-ue is calculated by comparing the number ofcarcinogens identified as mutagens to the totalnumber of both carcinogens and noncarcino-gens that were mutagenic. This means that morethan 90 percent of the substances detected asmutagens were carcinogens.

An important qualifier must be applied to thepredictive value of a test. It depends strongIynot only on sensitivity and specificity but alsoon the proportion of carcinogens in the collec-tion of substances tested for mutagenicity. Theproportion of carcinogens in both validation ex-periments shown in table 24 was well above 50percent.


Table 24.—Results Obtained in Two Validation Studies of the Ames Test WhenKnown Carcinogens and Noncarcinogens Were Tested

Results from:

Calculation a Bartsch et al. (22) McCann et al. (227)

Sensil ivity C+ M+ 760/o (62/82) 900/0 (156/174)c+ M+ + C+ M-

Speciiicity C- M- 570/0 ( 4/7 ) 880/0 ( 96H08)

C- M+ + C- M-

Predictive value C + M + 950/0 (62/65) 920/o (156/168)C+ M + + C- M +

Proportion of C + M + + C+ M- 920/o (82/89) 620/o (174/282)carcinogens all chemicals tested

a c + ~hemical~ known to be carcinogens; ~ - chemicals known to be noncarclnogensM + chemicals identified as mutagens; M chemicals identified as nonmutagensc + M + ~;arcinogens “correctly” identified aS I?IUta9enSC – M – noncarcinogens “correctly” identified as nonmutagensC – M + noncarcinogens “incorrectly” identified as mutagensC + M – carcinogens “incorrectly” identified as nonmutagens

SOURCE’ Office of Technology Assessment, adapted from Bartsch et al. (22)

Table 25 shows the expected results from ex-amining two hypothetical collections of chem-icals. The first collection of 1,000 chemicals con-tains 10 carcinogens (1 percent); the second con-tains 100 carcinogens in 1,000 total chemicals(10 percent). The short-term test in both cases isassumed to be 90-percent sensitive and 90-per-cent specific. The predictive value in the twocollections differs more than sixfold because ofthe higher contribution of false positives to thetotal positives in the l-percent carcinogen col-lection. This example illustrates the importantrole played in predictive value computations bythe percentage of carcinogens included in vali-dation experiments.

McMahon, Cline, and Thompson (233) devel-oped a modification of the Ames test and used itto assay 855 chemicals. To validate their owntest system, the authors included 125 chemicalsthat had been tested previously in the Ames test.They reported “excellent agreement” betweenresults in their tests and those reported byMcCann et al. (227), Among the other chemi-cals tested by McMahon, Cline, and Thompson(233) the 299 chosen from manufacturing orlaboratory synthesis provided the largest per-

centage of mutagens; 60 of 299 (20 percent) weremutagenic. In contrast, chemicals developed aspotential agricultural or pharmaceutical prod-ucts were less often mutagenic; 29 of 361 suchcompounds (6 percent) were positive. Theauthors state (233):

Very few of the chemical mutagens detected inthis study had chemical structures uniquely dif-ferent from known carcinogens. Further study inother test systems will be required to assess thesignificance of results with the few unique com-pounds encountered. The results of the study dosuggest, however, that as testing continues onmore and more compounds it will be found thatmost of the new mutagenic compounds detectedwill be related to known carcinogens and muta-gens and that new unique chemical structurespossessing these properties will be found rarely.

The McMahon, Cline, and Thompson paper(233) illustrates that large numbers of chemicalscan be tested quickly. Furthermore, theirresults, which are in “excellent agreement”with those earlier reported by McCann et al.(227) for chemicals tested in both studies, il-lustrate that the test is reproducible in differentlaboratories. Whether the prediction that most

Ch. 4—Methods for Detecting and Identifying Carcinogens ● 119

Table 25.—Expected Results of Examining Two Collections of Chemicals for Mutagenicity Using a Short-TermTest That is 90-Percent Sensitive and 90-Percent Specific: One Collection of Chemicals Contains 1 Percent

Carcinogens; the Other Contains 10 Percent

Proportion of carcinogens insample of 1,000 chemicals

Carcinogens identified asmutagens

Carcinogens identified as non-mutagens—false negatives inthe test

Noncarcinogens identified asnon mutagens

Noncarcinogens identified asmutagens—false positives inthe test

Summary:

Carcinogens identified asmutagens

Noncarcinogens identified asmutagens

Predictive value— carcinogensidentified as mutagens/totalcarcinogens plus noncarcinogensidentified as mutaqens

Calculation a

C+ M+ + C+ M -

all chemicals tested

C + M +

c+ M+ + C+ M-

C+ M -

C + M + + C+ M-

C- M-

C- M- + C- M+

C- M+

c- M- + C- M+

C + M +

C + M + + C- M +

Collections of chemicalswith

1 0/0 carcinogens 100/0 carcinogens

1 0/0 (i.e., 10 100/0 (i.e., 100carcinogens) carcinogens)

90°/0 (i.e., 9 of the 10 900/0 (i.e., 90 ofcarcinogens) carcinogens)

10°/0 (i.e., 1 of the 10 100/0 (i.e., 10 ofcarcinogens) carcinogens)

~oO/o (i.e., 891 of 990

non carcinogens)

100/0 (i.e., 99 of 990noncarcinogens)

9

99

108

8.3°\0 (i.e., 9I108)

the 100

the 100

~oO/o (i.e., 810 of ’0 0

noncarcinogens)

100/0 (i.e., 90 of 900noncarcinogens)

90

90180

50°/0 (i.e., 90H80)

a c + chemicals known to be carclno9ens; 2 – chemicals known to be noncarcinogens~ + Chemicals Identified as mutagens, M chemicals identified as nonmutagensC + M + carcinogens “correctly” Identlfled as mutagensc – M + noncarcinogens ‘r Incorrectly” Identlfled as mutagensC + M – carcinogens “incorrectly” Identlfled as nonmutagens

SOURCE Office of Technology Assessment, adapted from Bartsch et al (22)

mutagens will have structures related to those ofknown carcinogens awaits further testing.

The International Program for the Evaluationof Short-Term Tests for Carcinogenicity (par-tially supported by the National ToxicologyProgram (NTP), the National Institute of Envi-ronmental Health Sciences (NIEHS), and EPA)is analyzing the accuracy of about 30 short-termtest systems including the Ames test. The pro-gram distributed 42 coded carcinogens and non-carcinogens to 66 investigators, and the resultsof those studies will be published in 1981. Theaccuracy of the Ames test in the 12 laboratorieswhich examined it is comparable to the higher

accuracy figures (about 80 percent) in the litera-ture (188).

The largest program in genetic toxicology(mutagenicity) is EPA’s Genetox Program (357).It is not now engaged in validating short-termtests for predicting carcinogenicity, but it is ex-amining correlations among various short-termtests. Beginning in early 1982, the program ex-pects to publish recommendations for batteriesof tests most appropriate for measuring par-ticular mutagenic effects.

How much reliance is to be placed on theresults of short-term tests continues to be


discussed. Leon Golberg, former President ofthe Chemical Industry Institute of Toxicology(CIIT), for instance, compared the results fromAmes tests to bioassay results for hair dye com-ponents. He found little agreement and cautionsagainst using the Ames test as a substitute forbioassays (142,143). However, a recent paperfound good correlation between the mutagenici-ty and carcinogenicity of phenylenediamine hairdye components (330).

In summary, the Ames test is reported to de-tect known carcinogens as mutagens with a fre-quency as high as 90 percent. Although a break-through in understanding of the correlation be-tween mutagenicity and carcinogenicity is re-quired before more definitive conclusions can bedrawn from the Ames test, a positive Ames testresult shows that the agent is a mutagen andsuggests that it may be a carcinogen.

Other Short-Term Tests

The number of short-term tests has prolifer-ated rapidly. Purchase et al. (301) included onlysix short-term tests in a 1976 review of the pub-lished literature; less than 1 year later, OTA hadsaccharin tested in 12 short-term tests (282).Two years after that, in the summer of 1979, areview by Hollstein et al. (172) reported thatover 100 short-term tests had been described inthe scientific literature. The proliferation of testsreflects the great interest in cheaper, faster testsfor identifying chemical carcinogens.

Hollstein et al. (172) divided short-term testsinto eight classes, according to what they candetect:

1.

2.3.

4.5.

6.

mutagenesis in bacteria (including Salmo-nella) and bacterial viruses;mutagenesis in yeast;mutagenesis in cultured (laboratory-grown) mammalian cells;mutagenesis affecting mouse hair color;mutagenesis in fruit flies (Drosophila mel-anogaster);effects on chromosomal mechanics in in-tact mammals and in mammalian cells inculture;

7. disruption of DNA synthesis and DNA re-pair mechanisms in bacteria and otherorganisms; and

8. in vitro transformation of cultured cells.

One of the powerful tools available to biolo-gy is the use of cell culture systems, whichallows cells obtained from animal or human tis-sues to be grown and manipulated in the labora-tory. Cell cultures can be manipulated to serveas assays for mutagens (#3 above) and for chem-icals that interfere with chromosomal mechanics(#6 above), but the most directly applicable useof cultured cells for carcinogen identification in-volves in vitro transformation (#8 above).

Cells grown in culture exhibit characteristicmorphologies and growth patterns. Exposingcultured cells to known tumor-causing virusesor to chemical carcinogens causes changes inmorphology and growth characteristics. Thechanges are collectively called “transforma-tion. ” Transformed cells resemble cells fromtumors and have the important property ofcausing tumors when they are injected into ani-mals, thus demonstrating a direct relationshipbetween transformation and oncogenicity (tu-mor formation). Transformation of cell culturesis biologically more closely related to onco-genicity than is mutation, and transformationassays may take on major importance in testingprograms. The NTP 1979 Annual Plan (271)stated:

A lifetime bioassay in rodents is the currentprocedure utilized to determine carcinogenic po-tential of a chemical. The NTP does not proposealternative methods but acknowledges a need inthe longer term, to develop or validate less ex-pensive and more rapid methods that may insome instances supplant the need for lifetimebioassays. Mammalian cell transformations arepotential short-term assays that indicate car-cinogenic potential of a chemical . . .

And less than a year later, a more optimisticcomment appeared in the Department ofHealth, Education, and Welfare (DHEW) HealthResearch Planning document of December 1979(130):


The dimensions of NTP, and the significantdemands it places on the funds and personnel ofthe participating agencies, should diminish by1985, as the fiscal projections suggest . . . . It isour hope that, by then, better test systems willbegin to replace the tedious and costly animalassays now required.

Not everyone is so optimistic as to think a re-placement for animal assays will be available in4 or 5 years. Transformation tests are probablythe best bet for the replacement, but they re-quire more development and validation.

Transformation assays are technically moredifficult than the Ames test, but not so difficultas to preclude their use on a routine basis.Validation studies are being carried out on anumber of in vitro transformation systems todetermine how accurately they identify carcino-gens and noncarcinogens (271,272).

NTP is conducting additional validation stud-ies of a test that uses whole animals. This test,which has been in limited use for about 30years, requires about 6 months to complete. Ex-posure of a particular strain of mice to knowncarcinogens causes an increase in the frequencyof lung tumors (adenomas) and causes earlierappearance of the tumors. The test takes muchless time than the standard assay, and NTP(272) has found this test accurately predictsresults in bioassays. NTP tested 60 chemicals inthis system in 1980 and plans to test another 30in 1981.

The British publication The Economist (97)singled out a transformation assay, using Chi-nese hamster ovary cells, as having promise forcarcinogen identification. Discussion of short-term tests in that publication, which seldompublishes articles about biology, reflects the in-creasing importance of the tests. A more author-itative source, the NCI National Cancer Ad-visory Board’s Subcommittee on EnvironmentalCarcinogenesis (245) said: “ . . . this subcom-mittee is enthusiastic about the possible futureuse of in vitro [short-term] tests as part of ascreening system for potential carcinogens andbelieve that their further development and vali-dation deserve high priority.”

Use of Short-Term Test Results andPolicy Statements About the Tests

How best to utilize short-term tests in car-cinogen identification is hotly debated. The ma-jority view is that the tests are most useful as ascreen to determine a chemical’s potential car-cinogenicity. As a new chemical is developed oras an old one comes under suspicion, an inex-pensive short-term test or battery of tests canprovide information about whether it is or is notlikely to be a carcinogenic hazard. If the resultsof the test are negative, the chemical is consid-ered less likely to be a hazard than a chemicalthat is positive. In the case of a chemical beingcommercially developed, a positive result mightsuggest that the chemical not be produced orthat the cost of testing it in a bioassay should beconsidered in deciding whether or not to pro-duce it. A positive short-term test result on acommercially produced chemical most likelycauses more of a problem. The manufacturer isfaced with having to begin other tests and towarn his employees and customers of potentialhazard.

Opinions differ about the weight to be placedon short-term test results. Peter Hutt, formerGeneral Counsel at the Food and Drug Admin-istration (FDA), and now in private law practicesays that he advises his clients not to continuethe development of a product which is positivein a short-term test. He maintains that, “life istoo short” to invest time and effort in a chemicalthat is more likely than not to be considered asuspect carcinogen. Near the ether end of thespectrum of opinion, Leon Golberg, in review-ing poor correlations between results of Amestesting and bioassays of components of hairdyes, concludes “ . . . it is very hard to acceptthe fact that the Ames test is a predictor of car-cinogenic potential” (143).

The OSHA document “Identification, Classi-fication and Regulation of Potential Occupa-tional Carcinogens” (279), accepts the results ofshort-term tests as supportive evidence for de-ciding whether a chemical will be classified as acarcinogen or noncarcinogen. TSCA test stand-

122 Technologies for Determining Cancer Risks From the Environment

ards (106) and Federal Insecticide, Fungicide,and Rodenticide Act (FIFRA) guidelines (102)accept short-term tests as measures for muta-genicity but do not consider them in makingdecisions about carcinogenicity. However, theymention that test developments are promising.

An important step in making decisions aboutthe use of short-term tests are the ongoingvalidation studies which compare predictionsmade from short-term tests to knowledge aboutcarcinogenicity from bioassays or epidemiolo-gy. These studies, although limited by the qual-ity and quantity of data about carcinogenicity,are producing valuable information. In addi-tion, studies of molecular mechanisms of muta-genicity and carcinogenicity are important indeciding about the applicability of short-termtests.

BIOASSAYS

Chemicals cannot be tested for carcinogenici-ty in humans because of ethical considerations.A substantial body of experimentally derivedknowledge and the preponderance of expertopinion support the conclusion that testing ofchemicals in laboratory animals provides re-liable information about carcinogenicity.Animal tests employ whole mammal systems,and although they differ one from another, allmammals, including humans, share many bio-logical features (266):

Effects in animals, properly qualified, are ap-plicable to man. This premise underlies all ofexperimental biology and medicine, but becauseit is continually questioned with regard tohuman cancer, it is desirable to point out thatcancer in men and animals is strikingly similar.Virtually every form of human cancer has an ex-perimental counterpart, and every form of mul-ticellular organism is subject to cancer, includinginsects, fish, and plants. Although there are dif-ferences in susceptibility between different ani-mal species, and between individuals of the samestrain, carcinogenic chemicals will affect mosttest species, and there are large bodies of exper-imental data that indicate that exposures that are

The problem of the carcinogens that are notdetected (false negatives; lack of sensitivity) andthe noncarcinogens that are falsely detected(false positives; lack of specificity) by any onetest might be solved with additional short-termtests. The great attractiveness of a battery ofshort-term tests is that it might correctly iden-tify all carcinogens and noncarcinogens. Un-fortunately, no such battery has yet been de-fined. The composition of the battery will de-pend on validation studies and acceptance ofeach component test.

The growing use of short-term tests showsthat short-term tests have moved to an impor-tant position in toxicology. The speed withwhich they have been incorporated into Gov-ernment and private sector programs reflects theimportance of the need to which they are ad-dressed.

carcinogenic to animals are likely to be carcino-genic to man, and vice versa.

In comparison to short-term tests and epide-miology, bioassays have had a longer develop-ment period and enjoy greater acceptance thanthe short-term tests; they are more easily manip-ulated to produce evidence linking a particularsubstance to cancer than epidemiology, andthey can predict human risks rather than relyingon cases of human cancer to demonstrate risk.On the other hand, they take longer and costmuch more than short-term tests.

The bioassay’s apparent simplicity belies thedifficulty of executing such experiments. Brief-ly, the suspect chemical is administered to apopulation of laboratory animals. As animalsdie or are killed during the course of the study,they are examined for the presence of tumors.At the end of the treatment and observationperiod (generally about 2 years), the survivinganimals are killed and examined. A controlgroup of animals is treated exactly the same ex-cept that they are not exposed to the suspectsubstance. The type and number of tumors and

Ch. 4—Methods for Detecting and identifying Carcinogens ● 123

other relevant pathologies present in the ex-posed animals are compared with those in thecontrol group, and statistically analyzed.

A statistical expression commonly used to de-scribe a positive result is “. . . it has a p valueless than 0.05" (5 percent). The p value is theprobability that the observed effect might be ex-plained by chance; in this case, the expressionmeans that the probability of the observed car-cinogenic effect being due to chance is less than

5 percent. A p value of 0.05 or less is commonlyrequired to decide that a test result was statis-tically positive.

Finally a conclusion is drawn about whetheror not the evidence indicates that the substancecaused cancer in the exposed animals. An excel-lent discussion of experimental design andanalysis is available from the InternationalAgency for Research on Cancer (IARC) (187).

The first successful experimental induction ofcancer in animals (in 1915) showed that paintingrabbits’ ears with coal tar produced tumorswhich morphologically resembled human tu-mors associated with exposure to the same agent(cited in 342). Most chemicals which are pres-ently known to cause cancer in humans are alsocarcinogens in animals.

Verification of the predictive power of bio-assays would require that the agent be shown tobe a human carcinogen. Currently, IARC main-tains that convincing evidence for human car-cinogenicity is available for only 18 exposures,including 14 chemicals. At the same time, it lists142 substances for which data are “sufficient” toconclude that they are carcinogenic in animals.It is difficult to demonstrate human carcinoge-nicity. Once a substance is shown to be an ani-mal carcinogen, regulatory restrictions on andvoluntary reductions in the use of the chemicalmay reduce human exposures, making thosedemonstrations more difficult. Reductions in ex-posure in such cases are far more important tohuman health than the foregone opportunitiesto verify the predictive powers of bioassays.

Standard Protocols for Bioassays

An important event in bioassay design wasthe development of NCI’s Guidelines for Car-cinogenic Bioassay in Small Rodents (33 I). Theguidelines describe minimum requirements forthe design and conduct of a scientifically validbioassay and discuss important considerationsin undertaking such studies. They are written toprovide flexibility in experimental design whilesetting certain minimal requirements:

1.

2.

3.

4.

5.

6.

7.

Each chemical should be tested in at leasttwo species and both sexes. Rats and miceare usually the species of choice.Each bioassay should contain at least 50animals in each experimental group.When both sexes of two species are usedand two treatment levels are administeredand a third group is used as controls, a to-tal of 600 animals is needed (see table 26).Exposure to the chemical should startwhen the animals are 6 weeks old oryounger and continue for the greater partof their lifespan. Mice and rats are usuallyexposed for 24 months.One treatment group should receive themaximum tolerated dose (MTD), which isdefined as the highest dose that can begiven that would not alter the animals’normal lifespan from effects other thancancer. The other treatment group istreated with a fraction of MTD.The route by which a chemical is adminis-tered should be the same or as close aspossible to the one by which human ex-posure occurs.Animals are closely monitored through-out the study for signs of toxic effects andother causes affecting their health.Examination of animals is conducted byor under the direction of a pathologistqualified in laboratory animal pathology.

The guidelines also specify that special proce-dures (e.g., organ function tests, body burdendeterminations, absorption and excretion tests)may be needed for evaluating certain chemicals.


Table 26.—Distribution and Number of Animals ina Typical Bioassay Study of Carcinogens

Species A Species BExperimental groups Males Females Males Females

Dosage MTDa group 50 50 50 50Dosage MTD/x group 50 50 50 50Control group 50 50 50 50— —

aMaxlmum toterated dose.

SOURCE: National Cancer Institute

A National Research Council report (262)suggested a two-generation bioassay when thereis special concern with prenatal and perinatal ef-fects of a substance. In the suggested two-gen-eration experiment, the first generation is ex-posed from 6 weeks of age through their adultlife, including periods of reproductive activityand pregnancy, and the offspring are exposedfor their lifespans. The most important two-gen-eration experiments, from the standpoint ofpublic policy, were the three showing saccharinto be a bladder carcinogen in second generationrats (282). The advantage of the two-generationexperiment is that it exposes fetuses and veryyoung animals, which may represent the mostsensitive stages of life. This procedure costsmore and requires more time to complete thanthe one generation experiment. Probably be-cause of those disadvantages, it has not oftenbeen used.

Table 27 compares some specifics of NCIguidelines with those proposed by EPA fortesting under FIFRA (102) and TSCA (106). NCIguidelines state that at least two-dose levels betested; EPA requires three test doses. The high-est dose, high-dose level (HDL), for TSCA isdefined as being “slightly toxic” and is to bedetermined in a 90-day-feeding study to precedethe oncogenicity experiment. The other twodoses are to be fractions of HDL. EPA prefersthe term HDL, which is less specifically definedthan MTD, because of the controversies whichhave erupted over defining MTD. Three-doselevels are proposed by EPA because a review ofmany NCI bioassays revealed that tumor in-cidence was sometimes higher at a dose ofMTD/2 than at MTD because the higher dosekilled some animals before tumors might havedeveloped. The third-dose level will also pro-vide additional information about the dose-

response curve (102). The text which accom-panies the proposed EPA guidelines for carcino-gen testing under FIFRA (102) contains addi-tional information about alternative approachesconsidered and subsequently discarded for theguidelines.

Three to five years are required to complete abioassay. A subchronic test, to set dose levels,requiring 2 to 6 months, is followed by an aver-age 24 months of exposure to the agent, andsometimes an additional 3 to 6 months observa-tion period. Pathological examination of tissuesfrom the animals and evaluation of the patho-logical and other data may take an additionalyear.

The cost of a bioassay has been variously esti-mated: NCI estimates about $400,000, TSCAguidelines (106) estimated $400,000, and EPA(112) later estimated a range from $390,000 to$980,000 .

Some changes have been made in protocolssince the NCI guidelines were published, but incontrast to the situation in spring 1977, whenOTA reviewed carcinogen testing (282), appar-ently much less confusion and contention nowexist about what constitutes an adequate bio-assay. NCI guidelines are for minimal stand-ards; certainly larger populations of animals canbe tested. For very important bioassays, largernumbers of animals or more dosage groupsmight be specified.

Objections to the Usefulnessof Bioassays

Some general aspects of test design are seldomdisputed. Examples of such provisions are therequirement of a minimum number of animalsin the test groups and that (generally) both sexes

Ch. 4—Methods for Detecting and ldentifying Carcinogen 125

Table 27.—Guidelines for Bioassay in Small Rodents

— —— .- --NCI (331)a FIFRA (102) TSCA (106)

Endpoint

Study plan:Animal speciesNumber of animals ateach doseDosages

Dosing regimenStartEndObservation period

Organs and tissues to beexamined

Personnel qual i f icat ions:Study directorPathologistAnimal husbandry

Cost estimate

Carcinogenicity

2, rats and mice

50 males, 50 females2, MTD

MTD/2 or MTD/4plus no-dose control

At 6 weeks of ageAt 24 months of age3-6 months after end ofdosing

All animals: external andhistopathologic examination(ea. 30 organs and tissues)

N.s.Board-qualifiedN.s.

N.s.

Oncogenicity

2, rats and mice

50 males, 50 females3, MTD

MTD/2 or MTD/4MTD/4 or MTD/8

plus no-dose control

In utero or at 6 weeksMice, 18-24 mos; rats, 24-30N.s.

All animals: external exami-nation; some animals: path-ologic exam of 30 organsand tissues, other animals,fewer organs and tissues

N.s.N.s.N.s.

N.s.

Oncogenicity

2, rats and mice

50 males, 50 females3, HDL

HDL/2 or HDL/4HDL/4 or HDL/10

plus no-dose control

At 6 weeks of ageAt 24-30 months of ageN.s.

All animals: external andhistopathologic examination(ea. 30 organs and tissues)b

Responsibilities detailedBoard-certified or equivalentBoard-certified vet. orequivalent

$400,000 Y 160,000Abbreviations: MTD, Maximum tolerated dose, causes minor acute toxlclty

HDL, high dose level, causes some acute tox!cltyN s., not speclfled

a The NC I Guldellnes specify the lndl~ated m,nlmum requirements, Tfley a[lo~ for flexlblllty in experimental design so long as the minimum requirements are met,

b EPA estimates that the 40,000 microscope slldes produced In this examination WIII require more than 3/4 of a year of a pathologist’s time for analysls

SOURCE Off Ice of Technology Assessment

be tested. On the other hand, consensus doesnot exist about some aspects of experimentaldesign, for instance: How high a dose is to beadministered? The policy of the agency thatdraws up the guidelines is reflected in what itsays about the arguable aspects of experimentaldesign. Tomatis (341) has discussed five debatedissues about bioassay.

1. Doses of chemicals to which test animalsare exposed are too high and are not pre-dictive for effects at levels of human ex-posure.

High doses of suspect carcinogens are neces-sary to increase tumor incidence to a level thatcan be detected in the limited number of animalsused for tests (180). A chemical causing tumorsat a rate of 0.5 percent in the U.S. populationwould result in over 1 million cancer cases. Butan incidence of 0.5 percent would very probablygo undetected in the usual test population of 50

male plus 50 female rats or mice. Administra-tion of the chemical at a 10-times higher dosemight increase the response to a detectable levelgiven comparable sensitivity between the testanimals and humans. High doses are necessaryto increase the sensitivity of the tests, but argu-ments arise over whether or not a dose is so highthat it is not predictive of what happens at lowerdoses.

The biological argument against dependingon results at high doses centers on the conten-tion that such doses may alter metabolism orcause local irritations or other toxic responseand cause cancer through a pathway that wouldnot exist at lower doses (60,139,278). A solutionsometimes offered to the problems raised byhigh doses is to run bioassays with many moreanimals tested at lower doses. The most spec-tacular attempt at this was the National Centerfor Toxicological Research (NCTR) EDO1 study


which used 24,000 mice and was designed to de-tect one cancer in 100 animals. Unfortunately,neither it nor (probably) any experiment caneliminate the necessity for testing chemicals atdoses significantly higher than those experi-enced by humans. Even 24,000 is a smallnumber compared to the number of people ex-posed to many chemicals.

2. Routes of exposure in animal tests do notcorrespond to routes of human exposure.

Chemicals are administered to laboratory ani-mals in either food, water, by inhalation, force-feeding (gavage), skin-painting, or injection.Few objections are raised to administration infood, water, or by inhalation when the chosenroute mimics the route of human exposure.More objections are raised to gavage, skin-painting, injection, or ingestion when that is notthe normal human exposure route. However,such methods are sometimes necessary and, fur-thermore, carcinogens appear to be distributedthroughout the body regardless of the route ofexposure. EPA (106) stipulates that “to the ex-tent possible, route(s) of administration shouldbe comparable to expected or known routes ofhuman exposure.” Adherence to such sugges-tions will reduce the frequency of this objection.

3. Some animals used for testing are so bio-logically different from humans that re-sults from them have no value.

Choice of animals for bioassays represents acompromise. Most current guidelines require orsuggest that chemicals be tested in two rodentspecies, generally rats and mice. The advantagesof these species are their small size, reducing thespace necessary for housing, short lifespans (2to 3 years), reducing the time needed for a life-time study, and a large amount of informationabout the genetics, breeding, housing, andhealth of these animals. Rats and mice are cheapto buy, feed, and house, as compared withlarger animals.

Primates are sometimes used for certain toxi-cological testing. They are certainly more likehumans than rodents but their supply is limited.They are expensive, live up to 25 years, and re-quire large areas for housing. Despite these dif-ficulties, NCI now maintains about 600 mon-

keys for carcinogenicity testing at a cost ofabout $500,000 per year (2). Dogs are thoughtto be between rodents and monkeys in their ap-parent likeness to humans, but they are morelike primates in costs.

Differences in metabolism, bioaccumulation,and excretion between rodents and humansshould be considered in interpreting the sig-nificance of animal results for humans. There isno question that further research in the com-parative biochemistry and physiology of manand rodents is necessary, but the comparisonswill ultimately be limited by restrictions onwhat can be determined by experimentation inhumans. Moreover, metabolic studies haveshown that most differences between humansand experimental animals are quantitativerather than qualitative and support the idea thatanimal results can be used to predict humanresponses.

4. Some test animals or organs of test ani-mals are exquisitely sensitive to carcino-gens, and such sensitivity invalidates useof results from such animals.

Griesemer and Cueto (146) have analyzed theresults of testing 190 chemicals in the NCI Bio-assay Program (see discussion in Expert Reviewof Bioassay Results and app. A). They identified35 chemicals that were “strongly carcinogenic”in either the rat or the mouse and noncarcino-genic in the other species. Of the 35, 18 werepositive in the mouse and negative in the rat,and 17 were positive in the rat and negative inthe mouse, which indicates that neither animalwas much more often the sensitive species.However, 12 chemicals caused mouse liver tu-mors, no other lesion in the mouse and no le-sions in rats. Taken by themselves these resultssuggest that the mouse liver is a sensitive organ.

Liver tumors are often found in mice but areinfrequently found in U.S. citizens, althoughthey occur frequently in human populations inother parts of the world. Should a chemical thatcauses mouse liver tumors be considered a haz-ard? An approach to resolving the mouse liverquestion was to review how predictive such re-sults are for tumors in other animals. Tomatis,Partensky, and Montesano (343) showed posi-


tive correlation between a chemical’s beingoncogenic in the mouse liver and its being onco-genic either in the liver or at some other site inrats or hamsters. (Griesmer and Cueto (146)presented data only from rats and mice, andsome mouse liver carcinogens in their compila-tion might be positive in animals other thanrats. )

Despite the finding of Tomatis, Partensky,and Montesano (343) that mouse liver carcino-gens were often positive at other sites or in otheranimals, IARC (185,187) considers mouse liverand lung tumors as “limited evidence” for car-cinogenicit y. However, OSHA (272) acceptsmouse liver tumors as “indicators of carcinoge-nicity” if “scientific experience and judgment”are used in interpreting the data.

Crouch and Wilson (72) have analyzed someof the NCI Bioassay Program data. They cal-culated the potency and the standard error asso-ciated with potency of a chemical in causing atumor at a particular site in either the rat or themouse. In their analysis of 35 tested chemicals,they found that in 31 cases the potency in bothrats and mice agreed within a factor of 10. Theiranalysis and similar analysis by Ames et al.(14), which consider the inherent error in ex-periments and the sensitivity of experiments,significantly reduces the number of chemicalsthat are positive in one species and negative inanother. However, those analytical methodshave not been generally applied to bioassayresults.

5. Finding benign tumors in test animals hasno value in defining carcinogenicity.

Tumors can be divided into two classes,benign and malignant. Benign tumors do notmetastasize, the tumor cells remain in contactwith each other and do not invade other tissuesor organs. Malignant tumors can invade othertissues and metastasize, spreading to distantparts of the body and causing other tumors.Both types of tumors are found in experimentalanimals.

Hearings on pesticide regulations have beenmarked by repeated arguments about the im-portance of benign tumors. Should benigntumors found in experimental animals be takenas evidence that a chemical causes cancer?

The position that a benign tumor may laterbecome malignant, that the line of demarcationbetween benign and malignant is unclear, andthat benign tumors can also be life-threateninghas prevailed in regulatory agencies. Therefore,no distinction is made in regulatory decisionsbetween benign and malignant tumors. This isclearly reflected in FIFRA guidelines (102) andTSCA test standards (106) in which the end-point is oncogenicity (tumor causation) ratherthan carcinogenicity (which emphasizes malig-nancy) (see table 27).

Griesemer and Cueto (146) reported no dif-ficulty in deciding between benign and malig-nant tumors in the NCI Bioassay Program andthat their conclusions about carcinogenicitywere unaffected by including or excluding be-nign tumors. IARC statements reflect difficultiesin the interpretation of benign tumors. As men-tioned above, it considers the occurrence ofsome benign tumors as “limited evidence” forconcluding that a chemical is a carcinogen (185).It also states that “preneoplastic lesions” mayprogress to “frank malignancy.” Furthermore,IARC (186,187) considers that the occurrence ofboth preneoplastic and neoplastic lesions in thesame organ strengthens conclusions about car-cinogenicit y.

Expert Review of Bioassay Results

In addition to the general objections tobioassay procedures that have been discussed,specific objections may be raised to particulartests. For instance, animals may have been in-advertently exposed to more than one chemical,to pathogenic micro-organisms, to extreme tem-perature, or to temporary deprivation of foodor water, any one of which might influence re-sults. Another frequent item of contention iswhether or not a particular pathologic lesion in-dicates carcinogenicity. Critical reviews can re-duce concern that flaws in experimental designor conduct mar the experiment or bring its re-sults into question.

IARC periodically calls together panels of ex-perts to review the worldwide literature aboutthe carcinogenicity of particular chemicals orexposures. The IARC Monograph Program, be-


gun in 1970, had published reviews of bioassaysof 422 chemicals and processes by 1979. For 60of the 422 chemicals and processes, IARC wasable to evaluate both human and animal evi-dence for carcinogenicity. Those 60 are de-scribed in the epidemiology section below.

For the remaining 362 chemicals and proc-esses (185),

. . . there was no information available fromstudies in humans [but] the IARC was asked re-peatedly to consider making an assessment ofthe carcinogenic risk for humans which wasbased only on animal data.

In response to those requests, the IARC work-ing group recommended (185):

. . . that in the absence of adequate data in hu-mans it is reasonable, for practical purposes, toregard chemicals for which there is sufficient evi-dence of carcinogenicity (i.e. a causal associa-tion) in animals as if they presented a carcino-genic risk for humans (emphasis in original).

An IARC working group defined five cate-gories of evidence--sufficient, limited, inade-quate, negative, and no data—against which ex-perimental data are to be compared (see app.A). The working group decided that for 142chemicals there was sufficient evidence, forabout 100 there was limited evidence, and forthe remainder there was inadequate evidence forcarcinogenicity. The IARC exercise is especiallyimportant because it shows that experts fromboth the private and public sectors, sitting onIARC panels, can consider experiments and re-sults and reach decisions about their meaning.

Griesemer and Cueto (146) analyzed the re-sults of NCI's testing 190 chemicals. IARC (185)and Griesemer and Cueto (146) classificationsof chemicals included 33 chemicals in common.Analysis of the classification of those 33 (seeapp. A) shows that there was good agreementabout the more carcinogenic of the chemicals.Such agreement lends credence to the idea thattests carried out in different laboratories andanalyzed by different experts can lead to similarconclusions about carcinogenicity.

Policy Considerations About Bioassays

General acceptance of bioassays as predictorsof human risk is sometimes obscured by contro-versies about particular test results. The FederalGovernment, in response to controversies aris-ing from testing artificial sweeteners or pesti-cides, has asked a number of expert panels toconsider bioassay designs, results, and useful-ness. In all cases, the panels endorsed bioassayswhile reserving judgment about particular testsand attaching caveats to some results. Table 28is a listing of some Government-affiliated panelsand reports plus two trade associations, theAmerican Industrial Health Council (AIHC)and the Food Safety Council, and a union orga-nization which have commented on bioassays.

The Office of Science and Technology Policy(OSTP), in the Executive Office of the President(281) produced a good, brief exposition of meth-ods, a well-crafted list of recommendationsabout carcinogen testing, and suggestions for aFederal carcinogen policy. About bioassays, thereport says,

. . . it would seem prudent to view a positivetest result in a carefully designed and well-con-ducted mammalian study as evidence of poten-tial human carcinogenicity.

As indicated by the quote, some organizationsurge consideration of experimental design andexecution before drawing conclusions aboutcarcinogenicity. AIHC (8), in commenting onOSHA’s (278) proposed cancer policy, endorsedbioassays as predictors of human risk:

There is agreement further that a substancewhich is a confirmed oncogen in two mamma-lian species should be subject to regulation as aprobable human carcinogen.

All Federal regulatory agencies accept animaltest results as predictors of carcinogenic riskfor humans. The Interagency Regulatory Liai-son Group (IRLG) was formed in 1977 to alinethe policies of the Consumer Product SafetyCommission (CPSC), FDA, the Food Safety andQuality Service of the Department of Agricul-ture, EPA, and OSHA. IRLG stated (180):


Table 28-Some Organizations That Have Considered and Endorsed Animal Tests as Predictors ofHuman Risk From Chemical Carcinogens

Organization

The Secretary’s (HEW) Committee on Pesticides andtheir Relationship to Environmental Health

National Research Council

Office of Technology Assessment

National Cancer Advisory Board, Subcommittee onEnvironmental Carcinogenesis

American Industrial Health Council

Food Safety Council

Occupational Safety and Health Administration

Interagency Regulatory Liaison Group

Office of Science and Technology Policy

American Federation of Labor, Congress of IndustrialOrganizations, and United Steelworkers of America

——

—

—

————

—

—

——

—

—

—

Publication

Report (325)

Evaluating the Safety of Food Chemicals (259)Safety of Saccharin and Sodium Saccharin in the HumanDiet (261)Pest Control: An Assessment of Present and AlternativeTechnologies (262)Principles for Evaluating Chemicals in the Environment(263)Food Safety Policy (269)

Cancer Testing Technology and Saccharin (282)Environmental Contaminants in Food (284)

General Criteria for Assessing the Evidence for Carcino-genicity of Chemical Substances (245)The Relation of Bioassay Data on Chemicals to theAssessment of the Risk of Carcinogens for Humans UnderConditions of Low Exposure (246)

AIHC Recommended Alternative to OSHA’s Generic Car-cinogen Proposal (8)

Proposed System for Food Safety Assessment (125)

Identification, Classification and Regulation of PotentialOccupational Carcinogens (279)

Scientific Bases for Identification of Potential Carcinogensand Estimates of Risks (180)

Identification, Characterization and Control of PotentialHuman Carcinogens: A Framework for Federal Decision-making (281)

Post-Hearing Brief on OSHA’s Proposed Standard on theIdentification, Classification and Regulation of Toxic Sub-stances Posing a Potential Occupational CarcinogenicRisk (7)

SOURCE: Off Ice of Technology Assessment.

Evidence of the carcinogenic activity of anagent can be obtained from bioassays in experi-mental animals.

and,

Positive results, obtained in one species onlyare considered evidence of carcinogenicity. Posi-tive results in more limited tests (e.g., when theobservation period is considerably less than theanimal’s lifetime), but by experimentally ade-quate procedures, are acceptable as evidence ofcarcinogenicity. Negative results, on the otherhand, are not considered as evidence of lack of acarcinogenic effect, for operational purposes,unless minimum requirements have been met.

As these quotes show, both AIHC and IRLGaccept bioassays as predictors of potentialhuman risk. However, they differ in the weightof evidence each requires. AIHC wants positive

test results in two species before making deci-sions about carcinogenicity, while IRLG willconsider making a decision on the basis of posi-tive results in one species. Labor organizations(e.g., American Federation of Labor, Congressof Industrial Organizations, and United Steel-workers of America (7)) and environmentalgroups also consider positive results in a singleanimal as sufficient to make a judgment aboutcarcinogenicit y.

How Many Chemicals Are Carcinogensin Animal Tests?

The number of chemicals that are carcino-genic in humans or animals is uncertain. A fewestimates have been made, but the bases for theestimates are poor.


OSHA (279) states: “Most substances do notappear to be carcinogenic, ” and uses informa-tion from two lists of test results to support thestatement. OSHA cites the study of Innes et al.(176), which tested 120 industrial chemicals andpesticides. Eleven (less than ten percent) werereported to be carcinogenic, 20 were consideredto require further study, and 89 “did not givesignificant indication of tumorigenicity. ” A Na-tional Academy of Sciences review of pesticides(262) also drew attention to the low number ofpositive results reported in the Innes study. Thesmall number was judged to be especially signif-icant because of the large number of biologicallyactive pesticides included in the test. Certainreservations must be attached to these conclu-sions. The maximum dose tested and the num-ber of animals used in the experiments weresmaller than now required, and consequently,the experiments were less conclusive than morerecent ones.

A more direct criticism of relying on the Inneset al. (176) document as a measure of how manychemicals are carcinogens is that it was a pre-liminary report. Based on the complete report(26), Barnard (21) states that 29 percent of thetested compounds were carcinogenic.

The second source cited by OSHA (279) is theseven-volume Public Health Service (PHS) listof chemicals tested for carcinogenicity (298).OSHA (279) reported that about 17 percent ofthe 7,000 tested chemicals were tumorigenic.However, OSHA concluded that these data“overstated the true proportion of carcinogenicsubstances in the human environment” becausesuspicious chemicals are selected for testing.

Despite such reservations, the Task Force onEnvironmental Cancer, Heart and Lung Disease(339) said:

Of the upwards of 100,000 known chemicalsof potential toxicity, only approximately 6,000have been tested for carcinogenicity. It is esti-mated that 10 to 16 percent of the chemicals sotested provide some evidence of animal carcino-genicity.

To treat the reported 10 to 16 percent of testedchemicals as carcinogens as a reliable number isprobably an error because many of the 7,000

tests are clearly inadequate when measuredagainst current testing guidelines. Scientists em-ployed by the General Electric Co. (141a) havealso examined the lists from the seven volumes(298). Using a relaxed criterion for carcino-genicity “ . . . any listing that reported anincidence of tumors in the test animals higherthan in the control animals was scored as‘positive, ’ “ upwards of 80 percent of the listedchemicals were found to be positive. It isimportant to recognize that this relaxedcriterion would not be accepted in any regula-tory decision, and it exaggerates the number ofpositives. Furthermore, biases toward testingchemicals that are likely to be carcinogenic andtoward reporting positive results push thepercentage of positives upward.

OSHA (279) had a contractor analyze a list of2,400 suspect carcinogens compiled by the Na-tional Institute of Occupational Safety andHealth (NIOSH). The contractor estimated thatfor 570 (24 percent of the total) there were suffi-cient data to permit initiation of rulemaking toclassify them as category I or 11 carcinogensunder the proposed OSHA policy.

Neither the Innes study nor the PHS list pro-vides information as reliable as that which ismore recently available from NCI, IARC, andNTP. Fifty-two percent of NCI-tested and re-ported chemicals were carcinogens (146). Either“sufficient” or “limited” data existed to classifyabout 65 percent of IARC-listed chemicals ascarcinogens (186,344). NTP (273) reported that252 (including the 190 reported by Griesemerand Cueto (146)) tests have been completed inthe NCI Bioassay Program. Under conditions ofthe tests, 42 percent were positive, 9.5 percentwere equivocal, 36 percent were negative, and13 percent were inconclusive.

The biases toward testing likely-to-be-posi-tive chemicals cannot be ignored, and the factthat negative test results are less likely to bepublished and included in any compilation (279)further complicates analysis of lists of testedchemicals. These factors tend to increase thepercentage of positive chemicals, and conse-quently may inflate the estimates of the percent-ages of chemicals that are carcinogens.


A definitive answer to questions about how Finding more and more chemicals to be car-many chemicals are carcinogens would depend cinogenic in bioassays raises important policyon testing every chemical, and that is beyond questions and may force a decision to rank car-the capacity of the bioassay system. Tomatis cinogens for possible regulation or voluntary(341) reported that 828 chemicals were under reductions. It is not apparent how to deal with atest worldwide in governmental programs in large number of carcinogens without ordering1975, and that 317 were repeat tests of chemicals them according to their riskiness.for which, in his opinion, adequate data alreadyexisted. He did not estimate the number ofchemicals under test in private or commerciallaboratories.

SELECTION OF CHEMICALS FOR TESTING INBIOASSAYS AND SHORT-TERM TESTS

Tests develop information to aid in makingdecisions about chemicals, and the most impor-tant step in information development is placingthe chemical on test. Limited testing capacitymakes it necessary to pick and choose amongchemicals. Not all can be tested. The secondNTP Annual Report (272) underlines this pointin discussing bioassays:

It is unreasonable even to attempt to study all48,000 chemicals in this way. Current knownworld capacity permits the initiation of perhaps300 such chemical tests each year, and the resultspublished this year are from the tests begun 4 ormore years ago. This capacity—even if financialresources were not limiting—could be no morethan doubled in the next 5-10 years. At this rate,it would take an additional 80 years to study allcurrently existing chemicals. Further, approxi-mately 500 new chemicals are introduced intocommerce each year, and this would result in anadditional backlog of some 40,000 untestedchemicals.

The same report pinpoints Federal Governmenttesting capacity:

In carcinogenesis testing the NTP proposes tostart 75 new chemicals on the lifetime carcino-genicity bioassays in fiscal year 80. This is thesame as the level achieved in fiscal year 79 and isa two-fold increase over the rate of testing priorto the establishment of the program. [In fact, 50were started in fiscal year 1980; 30 are expectedin fiscal year 1981. ]

By spring 1980, thecentered its selection

Federal Government hadactivities on two pro-

grams, the Interagency Testing Committee(ITC), and the NTP Chemical Nomination andSelection Committee. ITC recommends chem-icals for testing to the EPA Administrator underjurisdiction of section 4 of TSCA (the ITC list)and NTP selects chemicals for testing by theFederal Government. In addition, NCTR andCIIT have also published criteria for testingsubstances.

The Interagency Testing Committee

Section 4(a) of TSCA stipulates that EPAissue a rule to require testing if an individualchemical or category of chemicals “may presentan unreasonable risk of injury to health or theenvironment . . . or will be produced in sub-stantial quantities and . . . enter the envi-ronment in substantial quantities or there is ormay be significant or substantial human expo-sure. ” The vagueness of such terminology, “un-reasonable risk, ” “substantial quantities, ” “sig-nificant or substantial human exposure, ” re-quires EPA to generate interpretations withinscientific, legal, and policy contexts.

Section 4(c) of TSCA established ITC to rec-ommend chemical substances or mixtures whichshould be given priority consideration for test-ing. ITC is composed of eight members, one


each from EPA, OSHA, the Council on Envi-ronmental Quality (CEQ), NIOSH, NIEHS,NCI, the National Science Foundation (NSF),and the Department of Commerce.

ITC is to give priority to those chemical sub-stances which are known or suspected to causeor to contribute to the causation of cancer (car-cinogens), mutations (mutagens),- or birth de-fects (teratogens). The total number of chemicalsubstances or mixtures recommended for testingat any one time is not to exceed 50. TSCA spec-ifies that ITC must update, as necessary, thetesting priority list at least every 6 months. TheEPA Administrator is directed to respond to achemical’s being placed on the list within 12months. The Administrator must either initiaterulemaking to require testing or publish reasonsfor not initiating a testing rule.

ITC’s initial selection of chemicals for con-sideration was made by combining about 20Government-compiled lists of potentially haz-ardous substances. Chemicals that did not comeunder TSCA’s purview were eliminated fromfurther consideration, and the remaining sub-stances were ranked against two measures: ex-posure and biological activity. The bases for de-termining exposure were explicitly specified byCongress in section 4(e)(i)(A) of TSCA:

● general population exposure (number ofpeople exposed, frequency of exposure, ex-posure intensity, penetrability);

quantity released into the environment(quantity released, persistence);

● production volume; and● occupational exposure.

In general, chemicals which were ranked highon the exposure scale were further rankedagainst biological activity measurements. TSCAspecified the first three factors, and the otherswere included because of their significance incharacterizing biological effects (183):

●

●

●

●

●

●

●

carcinogenicity,mutagenicity,teratogenicity,acute toxicity,other toxic effects,ecological effects, andbioaccumulation.

ITC examined the biological activity scoreand the individual biological and exposure fac-tors, and weighed the biological scores againstthe exposure scores to select chemicals for de-tailed reviews. After the reviews, chemicalswere recommended to the EPA Administratorfor consideration. A detailed description of thescoring system can be found in the initial ITCreport to the Administrator of the EPA (183).

As of November 1980, ITC had filed seven re-ports to the EPA Administrator. Each report hasupdated and revised the list of chemicals eligiblefor promulgation of test rules under section 4(a)of TSCA.

Chemical Categories

An important consideration in selectingchemicals for testing is how to deal with chem-ical categories or classes. Section 26(c) of TSCAspecifies that any action authorized or requiredunder the act “may be taken by the Administra-tor . . . with respect to a category of chemicalsubstances or mixtures [and] shall be deemed tobe a reference to each chemical substance ormixture in such category. ” In making its recom-mendations ITC selected some categories ofchemicals for testing. EPA must determinewhether to evaluate the scientific, economic,and regulatory consequences of every present orpotential member of a category of chemicals orto evaluate selected representatives from thecategory. If the decision is made to test repre-sentatives, EPA has to assess whether it could“reasonably” extrapolate test results to chem-icals within the group that have not beenstudied. Some industry representatives havequestioned the validity of using categories forchemical testing, particularly the categories rec-ommended by ITC. They express concern that itwould be unrealistic to establish a general policyfor choosing which chemicals should be testedfor every possible category. Charles Holds-worth, of the American Petroleum Institute,recommended that EPA select members of a cat-egory once the “metabolic actor” for the groupis determined. Another possible approachwould be to select chemicals of interest becauseof exposure or production volume.

Disposition of the ITC List

As of May 1981, 3-1/2 years after completionof the first ITC list, EPA had issued no final rulerequiring testing of any ITC-identified chem-icals. However, EPA (110) in the summer of1980 proposed its first health effects test rule onchemicals nominated by ITC. The proposed rulewould require testing of chloromethane and rep-resentative members of the category of chlori-nated benzenes for oncogenicity and otherhealth effects. Support documents describingthe reasons for deciding to require testing andan economic impact analysis of the tests werealso released (110,112). As of April 1, 1980,draft copies of test rules for four additionalchemicals and groups of chemicals from the 21identified on the first three ITC lists were avail-able from EPA.

The General Accounting Office (141) re-ported that EPA estimates it will take 5 years toissue a final test rule for an ITC-nominatedchemical. That time is required for the agency toevaluate the published information about thechemical. EPA further estimates that an addi-tional 4 years will be required for execution ofbioassay and analysis of their results. At aminimum, then, 9 years will pass between thedecision to test an ITC-selected chemical andcompletion of testing. Certainly the long timebetween the decision to require testing and theproduction of results is of concern to EPA, andthe agency is working to reduce it (141).

There is a suggestion that many ITC-selectedchemicals are currently under test in other armsof the executive branch. NTP (273) reportedthat of 20 single chemicals and 15 classes recom-mended by ITC (as of April 1980), 16 of the 20chemicals and representative chemicals from 14of 15 classes were then under test or scheduledfor test by NTP. NTP (273) did not make a com-parison between the types of tests recommendedby ITC and the types of tests being carried outor planned by NTP. The NTP report draws at-tention to a problem common to an active fieldsuch as toxicology. ITC judgments aboutwhether or not to require a test are based orwhat it knows about in-progress and completedtests. It is important that NTP and other testing

organizations share their latest information andplans with ITC. Accordingly, a liaison repre-sentative of NTP attends and participates in ITCmeetings and related activities.

Responsibility for Testing Under TSCA

Once a chemical or category is selected fortesting, EPA must determine who should bearthe responsibility and burden of testing. TSCArequires EPA to indicate whether manufac-turers, processors, or both manufacturers andprocessors bear the responsibility. EPA ispresently evaluating exposures that occur atvarious points in a chemical’s life cycle. If EPAfinds that the chemical’s manufacture may pre-sent a risk, only the manufacturers must test. Ifprocessing may pose a hazard, only the proces-sors are required to test. However, if distribu-tion in commerce, use, or disposal of the chemi-cal may present a risk, both the manufacturersand the processors are required to test. Thisdetermination has substantial economic andlegal ramifications since it will establish theuniverse of firms which must bear the cost oftesting. Some of the chemicals for which testrules have been drafted are manufactured bymore than one company. EPA is urging thatfirms cooperate to sponsor single tests of thechemicals rather than have each company spon-sor its own test.

National Toxicology Program

NTP was established within DHEW (now De-partment of Health and Human Services(DHHS)) on November 15, 1978, to further thedevelopment and validation of integrated tox-icological test methodologies. The NTP Ex-

ecutive Committee is composed of the heads ofFDA, OSHA, CPSC, EPA, National Institutesof Health (NIH), NIOSH, NCI, and NIEHS.

NTP’s annual plan for fiscal year 1980 (272)describes methods to select chemicals for test-ing: NTP operates under the principle that in-dustry will test chemicals for health and envi-ronmental effects as intended and mandated byCongress under legislative authorities. HOW-ever, some chemicals will not be tested by theprivate sector, and NTP will select chemicals for


its own testing program from the followingcategories:

1.

2.

3.

4.

5.

6.

7.

8.

chemicals found in the environment thatare not closely associated with commer-cial activities;desirable substitutes for existing chem-icals, particularly therapeutic agents, thatmight not be developed or tested withoutFederal involvement;chemicals that should be tested to improvescientific understanding of structure-activ-ity relationships and thereby assist in de-fining groups of commercial chemicalsthat should be tested by industry;certain chemicals tested by industry, or byothers, the additional testing of which bythe Federal Government is justified toverify the results;previously tested chemicals for whichother testing is desirable to cross-comparetesting methods;“old chemicals” with the potential for sig-nificant human exposure which are ofsocial importance but which generate toolittle revenue to support an adequate test-ing program (some of these may be“grandfathered” under FDA laws);two or more chemicals together, whencombined human exposure occurs (suchtesting probably cannot be required of in-dustry if the products of different compa-nies are involved); andin special situations, as determined by theexecutive committee, marketed chemicalswhich have potential for large scaleand/or intense human exposure, even if itmay be possible to require industry to per-form the testing.

NTP solicits lists of chemicals from NTP re-search (NCI, NIEHS, FDA, NIOSH) and regu-latory (FDA, OSHA, CPSC, EPA) agencies,other Federal agencies, academia, industry, la-bor, and the public. All of the chemicals sug-gested for study are funneled to the NTP Chem-ical Nominations Group.

The Chemical Nominations Group, com-posed of representatives from EPA, OSHA,FDA, CPSC, NIH, NCI, NIEHS, and NTP, pre-

pares a dossier describing what is known aboutthe physical properties of each chemical, its pro-duction volume, its use, exposures to it, and anytoxicological information, Each chemical isjudged against the chemical selection principlesdescribed above and nominations are forwardedto the NTP Executive Committee which makesfinal decisions about which chemicals to placeon test.

A decision by NTP to test a chemical does notmean necessarily that the chemical will beplaced on a bioassay program. It may mean thatthe chemical will be entered into less expensive,short-term tests first, and depending on theresults of those tests, subsequent decisions willbe made about whether testing should continue.

The National Center forToxicological Research

NCTR, a research arm of EPA and FDA wasestablished to develop a better understanding ofadverse health effects of potentially toxicchemicals. NCTR’s research emphasis is on de-termination of adverse health effects resultingfrom long-term, low-level exposure to chemicaltoxicants (food additives, residues of animaldrugs, etc.); determination of the basic biologi-cal processes involving chemical toxicants inanimals in order to enable better extrapolationof toxicological data from laboratory animals toman; and development of improved methodolo-gies and test protocols for evaluation of the safe-ty of chemical toxicants (good laboratory prac-tices, automated data systems, etc.). NCTRchooses substances for testing from the follow-ing categories (271):

1.

2.

substances that have no clear industrialsponsorship and for which it is determinedthat further toxicological data are needed.Usually these are either food contami-nants, GRAS (generally recognized as safefood additives) compounds, or cosmeticingredients.substances that can act as model com-pounds in a continuing toxicologicalmethods development program.


3. substances for which there is a pressingneed to acquire toxicological data aboveand beyond that which may be suppliedby industry.

4. studies as a direct regulatory response toconsumer complaints.

Chemical Industry Instituteof Toxicology

CIIT was established in 1974 as an independ-ent, nonprofit research laboratory financed byannual contributions from the member compa-nies. Membership in CIIT is open to any cor-poration or other business entity whose activityconsists to a substantial extent of the manufac-ture, processing, or use of chemicals and anyformal association of such entities. CIIT is toprovide objective study of toxicological prob-lems problems involved in the manufacture,

TIER TESTINGThis chapter has so far discussed various test

procedures, from quick, low-cost molecularstructure analysis through relatively quick,relatively cheap short-term tests to long-term,high-cost bioassays. The fourth category of test,epidemiologic studies, differs from the otherthree. Detection of a carcinogen because itcauses human illness and death can be regardedas a failure in hazard identification, because theother three tests should have or might have pre-dicted the risks before the substance had achance to inflict harm.

During the last several years, a number of ex-pert committees and panels have discussed anordered approach to testing—proceeding fromquick, cheap tests to longer, more expensivetests. One such “tier testing” plan was devel-oped by an expert group drawn from academicinstitutions, public-interest organizations, in-dustry and Government agencies (66). A re-peated criticism expressed in letters that com-mented on the plan was the absence of criteriaon which to drop a chemical from further test-ing requirements (66), The point was made thatthe tier system developed by the Conservation

handling, use, and disposal of commoditychemicals.

CIIT has developed a set of criteria to selectand rank chemicals into priority lists for study.These criteria are:

. volume of production,● physical and chemical properties,● estimated human exposure,● toxicological suspicion and opinion,● public interest, and● significance to society.

To date about 40 chemicals have been se-lected by CIIT for review and study. CIIT’stesting showed that formaldehyde caused nasalcancer in rats. Those results have been used byFederal agencies in considering regulationsabout the chemical.

Foundation was actually a sequential test series,since once a chemical entered the test series itwould apparently continue on through everytest.

Tier testing has no place in regulations of car-cinogens under FIFRA and TSCA, since EPAregulation of substances as a carcinogen re-quires bioassay or human data (102, 106). Totalk of a tier testing system under those regu-lations is academic, but evidently EPA is con-sidering a role for short-term tests for makingdecisions about carcinogenicity. In the suitbrought by the Natural Resources DefenseCouncil against EPA because of its failure to acton the ITC chemicals, Warren Muir of EPAsaid: “ . . . EPA is in the process of consideringwhat kinds of results from short-term tests sug-gest the need to require long-term tests for thepotential for causing cancer . . . “ (243).

An approach to tier testing appears in the1980 NTP annual plan and is described in figure20. The close interrelationships between genetictoxicology and carcinogenesis test programs areshown by the lines which connect them. The ab-


Figure 20.—lnterrelationships of Major Testing Activities of NTP

Phase IVPhase I Phase II Phase Ill Scientific and Public

Test program Identify toxic potential Confirm toxic effect More definitive result Health Assessment

I IGenetic toxicology Sa/nTone//a (Ames) assay (30~ EIrosophi/a spp ~ Mammalian assays S(mutagenicity) Mammalian cell culture (70) (30) (mouse heritable I I

N 7translocation)

I I

II Total evaluation

ICarclnogenesls Cell culture ~ Short-term in _ Lifetime rodent ~

of all data

tran:;formatlon wvo (mouse bloassays I

1

lung aaenoma) (75)

~1 i IToxicology Rodent toxicology

screen (75)

a ( ) ~earlY capacity, fiscal year 19E0 fi9ures.

SOURCE: Off Ice of Technology Assessment, adapted from NTP (272)

-+I

II

sence of arrowheads on the lines is intentional;according to David Rail, NTP Director (303),there has not yet been enough experience withthe scheme to be certain which phase I testsshould come first or whether all chemicalsshould go through all phase I tests.

A critical feature of tier testing is the ability tomake decisions about whether or not to con-tinue testing from phase I to II, or from 11 to III.Guidelines are necessary for making the deci-sion that a chemical is sufficiently without riskand that no further testing is necessary. Rail(303) said that development of decisionmakingguidelines is a priority item for NTP in 1980 and1981. NTP intends to analyze the testing his-

tories of chemicals that have gone through allthree phases (albeit not necessarily under NTPaegis) to determine which test results were mostpredictive of the ultimate decision about thechemical. NTP will take advantage of the factthat the most expensive and time consumingtesting, phase III, has been completed on somechemicals which have not otherwise been tested.Such chemicals will be entered into phase I andII testing to provide additional informationabout which tests are most predictive. Finally,the NTP decision to continue testing a fewchemicals that are negative in phase I tests willprovide additional information.

EPIDEMIOLOGY

Lilienfeld (210) defined epidemiology as the exposure to carcinogenic agents or between as-study of the distribution of disease in human pects of lifestyle and increased cancer risk.populations and of the factors that influence dis-ease distribution. Epidemiologic techniques are The earliest association of a factor withuseful for identifying causative agents and con- cancer was made by Ramazzini in 1713. Heditions that predispose for cancer. Studies can found that nuns had a higher rate of breastdetermine associations in populations between cancer than other women and, in his Treatie on

the Diseases of Tradesman of 1700, he at-tributed the increase to celibacy (322). Thatassociation has been sharpened to include theobservation that women who deliver a child atan early age are less likely to develop breastcancer. In addition to identifying cancer risks,epidemiology may play a positive role by poin-ting out less hazardous diets or agents which areprotective against cancer.

For the purpose of this discussion, epide-miologic studies are divided into three generaltypes: 1) experimental, 2) descriptive, and 3)observational. While several basic strategies ex-ist, there are no rigid study designs within anyof these categories. Flexibility is importantsince, unlike laboratory experiments, epidemi-ology examines groups of unpredictable peopleliving in dynamic environments. The impor-tance of flexibility is underlined by IRLG Guide-lines, which state that epidemiologic studydesign must “be described and justified in rela-tion to the stated objective of the study” (181).

Experimental Epidemiology

The ideal procedure for investigating cause-and-effect hypotheses is through experimentalepidemiology. This type of study requires thedeliberate application or withholding of a factorand observing the appearance or lack of appear-ance of any effect. Given the severity of cancer,ethical considerations preclude the administra-tion of suspected carcinogens to people, thoughit is possible to test agents thought to aid inprevention (292).

Experimental epidemiology studies are dif-ficult to conduct because of the need to securethe cooperation of a large group of people will-ing to permit an experimenter to intervene intheir lives. The investigator must have reason tobelieve that the proposed intervention, whethera deliberate application or withholding, will bebeneficial, but at the same time, he must besomewhat skeptical of the effects. Once suffi-cient evidence leads to the conclusion that theintervention is or is not beneficial, the experi-ment must be terminated.

Descriptive Epidemiology

Descriptive epidemiology studies examine thedistribution and extent of disease in populationsaccording to basic characteristics—e.g., age,sex, race, etc. The primary purpose of con-ducting descriptive epidemiologic studies is toprovide clues to the etiology of a disease whichmay then be investigated more thoroughlythrough more detailed studies. Descriptivestudies have focused on international com-parisons and comparisons among smaller geo-graphical regions, such as U.S. counties (29).

The identification of high bladder cancer ratesin New Jersey males and excess mortality ratesfrom cancer of the mouth and throat, esopha-gus, colon, rectum, larynx, and bladder in theindustrialized Northeast have suggested that oc-cupational factors might be incriminated andhave prompted additional investigations. Blotet al. (29) describe NCI’s stepwise approach tosearch for etiological clues. Examination of age-specific rates of disease occurrence or mortalityacross time (see ch. 2) is another example of de-scriptive epidemiology.

Observational Epidemiology

Observational epidemiology depends on dataderived from observations of individuals or rel-atively small groups of people. These studies areanalyzed using generally accepted statisticalmethods to determine if an association exists be-tween a factor and a disease and, if so, thestrength of the association. Often the hypothesisto be investigated arises from the results of a de-scriptive study. NCI has embarked on severalobservational studies based on findings fromtheir county-correlation studies. For example,high rates of lung cancer were found in theTidewater Virginia area, and a large study wasinitiated which found elevated risk for lungcancer in shipbuilders and smokers.

Cohort Studies

Two types of observational epidemiologystudies, cohort and case-control studies, differ

138 . Technologies for Determining Cancer Risks From the Environment

in the selection of the population groups forstudy.

A cohort study starts with a group of people,a cohort, considered free of the disease understudy, and whose disposition regarding the riskfactor under consideration is known. Usuallythe risk factor is an exposure to a suspect car-cinogen or a personal attribute or behavior. Thegroup is then studied over time and the healthstatus of the individual members observed. Thistype of study is sometimes referred to as“prospective” because it looks forward from ex-posure to development of the disease character-istic (210,225). Cohort studies can be eitherconcurrent or nonconcurrent in design. Concur-rent cohort studies depend on events which willoccur in the future, while nonconcurrent cohortstudies rely on past data or past events,

Case-Control Studies

In a case-control study, individuals with thedisease under study (cases) are compared to in-dividuals without the disease (controls) withrespect to risk factors which are judged rele-vant. Some authors label this study design“retrospective” because the presence or absenceof the predisposing risk factor is determined fora time in the past (210,225). However, in somecases the presence or absence of the factor andthe disease are ascertained simultaneously.

The choice of appropriate controls is rarelywithout problems. Often, for practical reasons,controls are chosen from hospital records. How-ever, they may not be representative of the pop-ulation, and they therefore may introduce “se-lection bias,” as discussed by MacMahon andPugh (218).

In case-control and cohort studies, the groupsselected should be comparable in all characteris-tics except the factor under investigation. Incase-control studies, the groups should resembleeach other except for the presence of the disease,while in cohort studies, the study and compari-son groups should be similar except for expo-sure to the suspect factor. Since this rarely ispossible in practice, comparability betweengroups can be improved by either matching in-dividual cases and controls (in case-control

studies) or by standard statistical adjustmentprocedures (in either case-control or cohortstudies). Demographic variables, e.g., age, sex,race, socioeconomic status, are most commonlyused for adjustment or matching.

There are advantages and disadvantages withboth the case-control and cohort studies (seetable 29). Case-control studies tend to be less ex-pensive to conduct, require relatively fewer in-dividuals, and many have been especially usefulin studying cancer. The great advantage ofcohort studies is that they allow observation ofall outcomes, not only those originally antic-ipated. Bias is somewhat reduced in cohort stud-ies since classification into an exposure categorycannot be influenced by prior knowledge thatthe disease exists. In a concurrent cohort study,it is often necessary to wait many years for themanifestation of enough disease cases to con-duct an analysis. The cost and time of the studycan be reduced if conducted nonconcurrently.Cohort studies tend to require many more sub-jects than case-control studies and assignment ofindividuals to the correct cohort for analysis isdifficult.

Causal Associations

A pragmatic view of causality is necessary,particularly when studying complex, multifac-torial diseases such as cancer. Analysis of theassociation between exposure and disease in anepidemiologic study depends on tests of statisti-cal significance. However, finding a positivestatistically significant association is not suffi-cient to conclude a causal relationship. Arti-factual and indirect associations must be con-sidered. As MacMahon and Pugh (218) state," . . . only a minority of statistical associationsare causal within the sense of the definition,which requires that change in one party to theassociation alters the other. ”

Policy Considerations AboutEpidemiology

While short-term tests and bioassays are usedto evaluate a chemical’s carcinogenic potentialin the laboratory, the effect on humans is direct-


Table 29.—Advantages and Disadvantages of Case-Control and Cohort Studies

Type of study Advantages Disadvantages

Case-control Relatively inexpensive Complete information about past exposures oftenunavailable

Smaller number of subjects Biassed recall

Relatively quick results Problems of selecting control group and matchingvariables

Suitable for rare diseases Yields only relative risk

Cohort Lack of bias in ascertainment of risk factor status Possible bias in ascertainment of disease

Yields incidence rates as well as relative risk Large numbers of subjects required

Can yield associations with other diseases as by- Long follow-up periodproduct

Problem of attrition

Changes over time in criteria and methods

Very costly

Difficulties in assigning people to correct cohort

SOURCE Office of Technology Assessment

ly assessed by epidemiologic techniques. Well-conducted and properly evaluated epidemiologystudies which show a positive association areaccepted as the most convincing evidence abouthuman risks.

Negative epidemiologic results show that ex-posure of a certain number of people to a sub-stance at a specified level did not cause cancer.From such results, it is possible to calculate thathuman risk is no higher than what the studycould have detected. For instance, a study of1,000 people which showed no excess cancerwould be “more negative” than one of 100 peo-ple exposed at the same level. Neither studywould show that a risk exists, and neither showsthat no risk exists, but the larger study shows alower probability of risk.

The OSHA Generic Cancer Policy (279) pro-posed that OSHA, after ascertaining the ade-quacy of the study design, would interpretnegative epidemiologic studies as setting an up-per limit for human risk. AIHC (8) wants nega-tive human evidence to be considered alongwith animal data in making decisions about car-cinogenicity. The OSHA position, and that ofFederal Government regulatory agencies in gen-eral (306), is to use epidemiology to estimatelimits of risk, but not to weigh negative humanevidence against other positive evidence in

deciding whether or not a substance is a car-cinogen.

The Regulatory Council (306) considers prop-erly designed and conducted epidemiologicstudies, which show a significant statistical re-lationship between human exposure to a sub-stance and increased cancer risk, to provide“good evidence” that a substance is carcino-genic. The Council mentioned some difficultiesin epidemiology, e.g., long latency periods,multiplicity of exposures, and cautioned thatoften “even large increases (which could involvethousands of people) . . . cannot be detected. ”For these reasons they cite two caveats in usingepidemiological studies:

The failure of an epidemiological study to de-tect an association between the occurrence ofcancer and exposure to a specific substanceshould not be taken to indicate necessarily thatthe substance is not carcinogenic.

Because it is unacceptable to allow exposureto potential carcinogens to continue until humancancer actually occurs, regulatory agenciesshould not wait for epidemiological evidencebefore taking action to limit human exposure tochemicals considered to be carcinogenic.

OSTP (281) states that “a positive finding in awell-conducted epidemiologic study can beviewed as strong evidence that a chemical poses

140 Technologies for Determining Career Risks From the Environment

a carcinogenic risk to humans. ” Alternatively,“a negative finding is not nearly so meaning-ful . . . “ and OSTP emphasizes the importanceof examining the sensitivity of a negative study,and suggests that the upper limit of risk thatmight have gone undetected in the study becalculated and presented.

Carcinogens for Which There IsHuman Evidence

Through various means, epidemiologic stud-ies have identified several human carcinogens.The first use of epidemiologic principles torelate environmental contaminants to humancancer is credited to Pott in 1775 (322). Pott, aphysician in London, suggested that scrotal can-cers, which he observed in men who hadworked as chimney sweeps when boys, werecaused by exposure to soot. Pott is an exampleof an astute physician recognizing an unusualcluster of cancer cases. A more recent example isvinyl chloride which was identified as a carcino-gen after three cases of a rare liver tumor(hepatic angiosarcoma) were diagnosed inworkers in a manufacturing plant (71). In thecase of vinyl chloride, evidence for its carcino-genicity in laboratory animals was available inadvance of the human evidence. In both cases,control action followed the demonstration ofoccupational risk. The Danish Chimney SweepsGuild instructed its members about protectiveclothing and to practice preventive hygiene soonafter Pott’s report was published, and OSHAregulated vinyl chloride.

IARC bases its evaluation of carcinogenic riskto humans on consideration of both epidemi-ological and experimental animal evidence.IARC considered human evidence bearing on 60chemicals and industrial processes and classified18 as human carcinogens (see table 30). Many ofthe human data considered by IARC are fromstudies concerning workplace and medical ex-posure. This does not necessarily reflect thedistribution of carcinogens but more likely thehigher exposure and relative ease of performingepidemiologic studies on patients and occupa-tional groups. For instance, the availability ofmedical records facilitates locating people ex-

posed to a drug and provides information abouttime of exposure and dose level.

IARC also classified 18 additional compoundsas probably carcinogenic for humans but therewas insufficient evidence to establish causalassociations. These 18 were further subdividedaccording to the degree of evidence, high orlow, as displayed in table 30. Insufficient evi-dence was available to decide about the carci-nogenicity of 18 chemicals listed in table 30.Finally, because of time limitations, IARC wasunable to evaluate six compounds for whichhuman data exist.

Annual Report on Carcinogens

In an effort to provide information on car-cinogens which would be useful to regulatoryagencies, Congress passed an amendment to theCommunity Mental Health Act (Public Law 95-622). It requires the Secretary of DHHS to pub-lish an annual report containing a list of sub-stances which are known to be carcinogens ormay reasonably be anticipated to be carcino-gens and to which a significant number of per-sons residing in the United States are exposed.The task was assigned to NTP, and the first re-port (82) includes the 26 exposures which IARChad determined in 1978 to be human carcino-gens (344). Candidates for the 1981 and 1982 listalso will be drawn from IARC beginning withchemicals and processes judged “probably carci-nogenic for humans. ” The initial report did not,as required by the statute, list “ . . . all sub-stances which either are known . . . or . . .may reasonably be anticipated to be carcino-gens . . . . “

One limitation enumerated in the first reportwas that, “Science and society have not arrivedat a final consensus on the definition of carcino-gen either in human populations or in experi-mental animals. ” The report, by includingchemicals and industrial processes already clas-sified by IARC, has sidestepped dealing with thequestion of what is a carcinogen. A definitionfor “carcinogen” remains elusive unless it isgiven in the context of a particular methodol-ogy.


Table 30.—Chemicals and Industrial Processes Evaluated for Human Carcinogenicity by the InternationalAgency for Research on Cancer (IARC)

Chemicals and processes judged carcinogenic for humans

4-aminobiphenyl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . c .. ..0. “ 0. “ . . P “ 0. “ . ~ . .Arsenic and certain arsenic compounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . “ . . .Asbestos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 0..... . . “ 0.0 “ “ ..0. “ 0. “ ..0.Manufacture of auramine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.0 “ . . . “ . “ 0 . . . .Benzene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...........”.”....” ““””.””.””.”.Benzidine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ““.......””.”.”..”..”” “.N,N-bis (2-chloroethyl)-2-naphthylamine (chlornaphazine) . . . . . . . . . . . . . . . . . . . . . . . . . . .Bis(chloromethyl)ether and technical grade chloromethyl methyl ether . . . . . . . . . . . . . . . . .Chromium and certain chromium compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......Diethylstilboestrol (DES). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......”..”..”.”” .“.Underground hematite mining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .........”””.””.. ““Manufacture of isopropyl alcohol by the strong acid process . . . . . . . . . . . . . . . . . . . . . . . . .Melphalan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .....,.-.”.”..”..””” “...”..”.*.oMustard gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .“..”””.o”c”.”.””.”.o2-naphthylamine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .........”.”...””. “...”...’”<Nickel refining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ““”..””....”.. -.Soots, tars and mineral oils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .....””...”..”.””Vinyl chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...”....”..”””..”’””. “.

Chemicals and processes judged probably carcinogenic for humansGroup A: Chemicals and processes with “higher degrees of evidence.”

Aflatoxins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......”...”””. .“’””..”....””... “..Cadmium and certain cadmium compounds . . . . . . . . . . . . . . . . ...........”...” ...”...Chlorambucil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .“......”...”””- ..””.Cyclophosphamide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..”.”.......”..”Nickel and certain nickel compounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . .Tris(1-aziridinyl)phosphine sulphide (thiotepa) . . . . . . . . . . . . . . ..;.... . . . . . . . . . . . ..”

Group B: Chemicals and processes with “Iower degrees of evidence.”

Acrylonitrile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....’.”.”...”..”.. “..”.”....””””Amitrole (aminotriazole) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...”..”....Auramine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .........”,..’’... ....”.....Beryllium and certain beryllium compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Carbon tetrachloride . . . . . . . . . . . . . . . . . . . . . . ................o....o .“..””..””....Dimethylcarbamoyl chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .........”.””.” ....Dimethylsulphate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......”......”.”””.”. .Ethylene oxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..”.”.....””.”.......”Iron dextran . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....”,........... ““.”””.”.”..”Oxymetholone . . . . . . . . . . . . . . . . . . . . . . ........o.o.....”’”o.”. “.”..””..”...”..- ..Phenacetin . . . . . . . . . . . . . . . . . . . . . . ..........,.,”....”.. ....”..”..””””.”.””””. “Polychlorinated biphenyls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....”........... ...”.

Degree of evidence

ExperimentalHumans animals

Sufficient SufficientSufficient InadequateSufficient SufficientSufficient NonapplicableSufficient InadequateSufficient SufficientSufficient LimitedSufficient SufficientSufficient SufficientSufficient SufficientSufficient NonapplicableSufficient Not applicableSufficient SufficientSufficient LimitedSufficient SufficientSufficient NonapplicableSufficient SufficientSufficient Sufficient

Degree of evidence


Limited SufficientLimited SufficientLimited SufficientLimited SufficientLimited SufficientLimited Sufficient

Degree of evidence


Limited SufficientInadequate SufficientLimited LimitedLimited SufficientInadequate SufficientInadequate SufficientInadequate SufficientLimited InadequateInadequate SufficientLimited No dataLimited LimitedInadequate Sufficient

Chemicals and processes that could not be classified as to their carcinogenicity for humansDegree of evidence


Chloramphenicol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ““”..”””. Inadequate No dataChlordane/heptachlor . . . . . . . . . . . . . . . . . . . . . . . . . . . ........c....o.”0”..o”.. .“.”””. Inadequate LimitedChloroprene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....”’”””..”..””.”””.. Inadequate Inadequate

—.


Table 30.—Chemicals and Industrial Processes Evaluated for Human Carcinogenicity by the InternationalAgency for Research on Cancer (IARC) (Continued)

Chemicals and processes that could not be classified as to their carcinogenicityDegree of evidence

for humans—continued ExperimentalHumans animals

Dichlorodiphenyl trichloroethane (DDT). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Dieldrin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Epichlorohydrin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... , . . . . . . . . . . . . . . . . . . . .Hematite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Hexachlorocyclohexane (technical grade HCH/lindane). . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Isoniazid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Isopropyl oils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Lead and certain Iead compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Phenobarbitone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .N-phenyl-2-naphthylamine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Phenytoin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Reserpine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Styrene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Trichloroethylene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Tris(aziridinyl)-para-benzoquinone (triaziquone) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

InadequateInadequateInadequateInadequateInadequateInadequateInadequateInadequate

LimitedInadequateLimitedInadequateInadequateInadequateInadequate

LimitedLimitedLimitedNegativeLimitedLimitedInadequateSufficient (forsome solublesalts)LimitedInadequateLimitedInadequateLimitedLimitedLimited

Chemicals and processes for which human data are available, but which were not considered by the IARC Working GroupOrtho-and para-dichlorobenzeneDichlorobenzidinePhenylbutazone2,3,7,8-tetrachlorodiberzo-para-dioxin (TCDD, the ’’dioxin” of Agent Orange)Ortho-and para-toluidineVinylidene chloride

SOURCE: Office of Technology Ajsessmen~ adapted from IARC (185)

SOURCES OF EPIDEMIOLOGICALLY USEFUL DATA

Three major types of information are usefulin assessing the carcinogenic risk of a substance:l) health status of exposed and unexposed pop-ulations; 2) exposure data; and 3) physical,chemical, and biological properties of the sub-stance. Information related to each of these cate-gories can come from a variety of sources andcan be used in different ways. Testing the sub-stance generates information about its potentialhazard, but information about its distribution inthe environment and any impacts on humanhealth are necessary to describe its human risk

Health Status Information

DHHS is primarily responsible for adminis-tering health data collection, storage, and anal-ysis projects. An overview of existing DHHSprograms and other departments’ health datacollection activities can be found in SelectedTopics in Federal Health Statistics (283).

National Center for Health Statistics

The National Center for Health Statistics(NCHS) located within the DHHS Office ofHealth, Research, Statistics, and Technology,was established to collect and disseminate dataon the health of Americans. Since 1960, it hasplayed a major role in the development of na-tional health statistics policy and programs. TheNCHS Division of Vital Statistics collects infer-mation on natality, mortality, marriage, anddivorce from the individual states and regions.(See ch.2 for a discussion of cancer mortalityand incidence statistics.) In addition to vitalstatistics, NCHS conducts several general-pur-pose surveys that provide statistics about thehealth status of the U.S. population. Additionalinformation can be obtained from Data Systemsof the National Center for Health Statistics(253).


Health Interview Survey (HIS) .–HIS is theprincipal source of information on the health ofthe civilian noninstitutionalized population ofthe United States. Initiated in 1957, interviewsare conducted each week in a probability sam-ple of households to provide data on a range ofhealth measures, including the incidence of ill-ness and accidental injuries, the prevalence ofdiseases and impairments, the extent of disabili-ty, and the use of health care services. Eachyear, approximately 40,000 households contain-ing about 120,000 persons are sampled.

HIS collects information only about condi-tions which respondents are willing to report.The basic questionnaires are similar from yearto year but supplemental questions may beadded. In 1978 and 1979 questions on smokingwere added, but these were discontinued in1980.

The NCHS Study of Costs of Environment-Related Health Effects, mandated by Public Law95-623, may use HIS as a data source (179).

Health and Nutrition Examination Survey(HANES).–HANES, initiated in 1970, is amodification and expansion of the earlier HealthExamination Survey (HES). These surveys col-lect and use data from interviews and physicalexaminations to estimate the prevalence ofchronic diseases, establish physiological stand-ards for various tests, determine the nutritionalstatus of the population, and assess exposurelevels to certain environmental substances. Thesampling techniques employed provide rep-resentative national data. Two surveys, HANESI (1971-75) and HANES II (1976-79) have beenconducted. Both surveys examined approx-imately 20,000 persons.

HANES is the most extensive national assess-ment of health and nutritional status of theAmerican people. The nutritional component ofHANES includes: information on dietary in-take; data from hematologic and biochemicaltests; body measurements; and chemical exam-ination for various signs of high risks of nutri-tional deficiency. Preliminary findings from theHANES II pesticide monitoring program have

found an apparent rise in tissue levels of DDTand PCBs. The implications of the observedlevels are uncertain.

HANES surveys might become valuablesources of information for cancer epidemiologyif sufficient resources were available. Because ofits representative nature, aggregate data fromthe survey can be used to represent “normal” orbackground levels. For example, white cellcount levels determined in HANES I were usedfor comparative purposes in an epidemiologicstudy of laboratory workers exposed to sus-pected toxic chemicals. HANES II contains cer-tain information about dietary intake of sub-stances which have been associated with a lowerrisk of cancer, vitamins A and C, and sub-stances such as fats which are associated withhigher risks.

HANES might be linked with other healthdata systems, such as the National Death Index(see below) to facilitate assessment of whetherparticular exposure levels or certain nutritionalstatuses were associated with cancer mortality.NCHS, with its HANES capabilities, has beenasked to participate in studies near Love Canal,and to evaluate the health status of certain high-risk industry groups. It was unable to do sobecause of limited resources.

The NCHS overall monitoring survey budgetfor fiscal year 1981 is $28 million. This is a $3million increase over 1980 and includes $1.1million for a special HANES study which willfocus on Hispanics in selected areas of theUnited States. The study is designed to describethe health and nutritional status of the Mexican-American, Puerto Rican-American and Cuban-American populations. Studies of specificgroups are necessary to acquire data in suf-ficient detail to describe subgroups of the pop-ulation which differ from the “average.” Gen-eral national surveys such as HANES I and IIproduce data about the “average” citizen bysampling groups in proportion to their repre-sentation in the total population, and this oftenresults in too small a sample size to be useful foridentifiable smaller groups.


As examples of data useful for cancer studies,the HANES Hispanic study will determine:

● name, date of birth, and social securitynumber recorded in machine readable formfor subsequent use with the National DeathIndex;

● history of toxic substance exposure;● nutritional status including dietary inter-

views, serum vitamin A levels, prevalenceof vitamin C deficiencies; and

the quantity and frequency of alcohol con-sumption.

Hospital Discharge Survey .—This surveywas established in 1964 to provide representa-tive statistics for the U.S. population dischargedfrom short-term hospitals. The survey collectsinformation on the characteristics of patients,the lengths of stay, diagnosis and surgical oper-ations, and patterns of use of care. Completionof each medical abstract form is estimated totake approximately 5 minutes. Only short-stayhospitals with six or more beds and with anaverage length of stay of less than 30 days areincluded in the sample (177).

Vital Statistics Followback Surveys. —NCHS-conducted mortality “followback” surveys haveprovided information on possible relations be-tween environmental and lifestyle factors anddeath from cancer. Information is sought aboutdecedents through inquiries addressed to thoseproviding information for the death certificate,such as the medical certifiers, funeral directors,and family members. These surveys are an effi-cient means to augment the routinely reportedinformation contained in the vital records.

The efficiency of the followback approach foreliciting additional information about deaths isrelated to the relative rareness of death as anevent in the U.S. population. About 1 percent ofthe population dies annually; and cancer-relateddeaths are reported for about 20 percent of this1 percent, or a total of 0.2 percent of the totalpopulation. The followback approach permitssampling directly from the file of those deathcertificates of interest in order to supplementexisting information.

Mortality followback surveys were con-ducted in the United States annually from 1961

through 1968. They have since been discon-tinued due to inadequate resources, includingpersonnel.

National Death Index (NDI).—Deaths in theUnited States are registered by the States orother death registration areas (e.g., District ofColumbia). The records are transmitted on mi-crofilms or on magnetic tape to NCHS for com-pilation. Historically, because there was no inte-gration of records for the country as a whole, nomechanism had existed at the national level todetermine if a person had died. In 1981, afterseveral years of planning and preparation, theNDI will be placed into operation to serve thatpurpose. The NDI will code deaths that oc-curred in 1979 and each year thereafter. Al-though there has been discussion of codingdeaths that occurred before 1979, no plans arenow in place to do so.

NDI, administered by NCHS, is designed toprovide medical and health researchers withprobable fact of death, the death certificatenumber, and the location of the death certifi-cate, when supplied with a minimum set of iden-tifiers (generally the person’s name and socialsecurity number or date of birth). The re-searcher then may contact the registration areawhere the possible match has occurred to obtainthe death certificate or the required infor-mation.

NDI will be of immediate use in ongoing long-term studies which include mortality. Beebe (23)described the NDI as the most important recentadvance in making vital statistics accessible toresearchers. NCI’s Surveillance, Epidemiology,and End Results (SEER) program plans to usethe NDI to determine deaths of all persons in theSEER registries. This should reduce the numberof people lost to followup by SEER and providebetter information about survival. Currently,deaths of people who moved or cease to partici-pate are not always recorded by SEER.

National Cancer Institute

NCI, 1 of 11 research organizations of NIH,receives more than one-fifth of all Federal healthresearch funds (283). NCI operates the SEERprogram, which provides cancer incidence data

on approximately 10 percent of the population.Additional information on the SEER programcan be found in chapter 2.

Centers for Disease Control

The overall mission of the Centers for DiseaseControl (CDC) (56) is “to prevent unnecessaryillness and death and to enhance the health ofthe American people. ” CDC serves as a focusfor DHHS efforts in the areas of disease preven-tion and control, environmental health, healthpromotion, and health education.

NIOSH, located within CDC, assists OSHAin establishing workplace health standards. Be-tween 1972 and 1974, NIOSH conducted theNational Occupational Hazard Survey (NOHS)to provide estimates of the proportion of em-ployees exposed to potential health hazards invarious industries. NOHS estimates of exposureare often used in assessing risks from occupa-tional carcinogens. NIOSH periodically con-ducts studies to identify the health effects of par-ticular industrial processes and to determine thehealth experience of selected employee pop-ulations. The National Surveillance Network,which is operated by NIOSH, collects data fromState safety and health inspection programs.

Social Security Administration

The Social Security Administration (SSA)collects information on economic and demo-graphic data in administering the social securitysystem. SSA makes available an annual l-per-cent continuous work-history sample (CWHS)to outside users which provides informationabout employment, migration, and earningstatus. Six different types of files, all of whichcontain sex, race, and age data, are available tooutside users. For purposes of confidentiality,the employee and employer identification areincluded in scrambled form. The usefulness ofthe CWHS for epidemiologic studies is limitedby privacy constraints of access and other char-acteristics, e.g., only wages UP to the taxablemaximum are reported.

SSA has recently initiated efforts to amass a10-percent sample of the work force because ofthe Office of Management and Budget’s (OMB)

need for better estimates of intercensal popula-tion. This file would constitute the most detailedinformation on the structure of the labor forceso that employment distributions by sex, race,age, wages, and wage changes, work force par-ticipation, industry, and regional migration pat-terns could be analyzed systematically.

The Disability Insurance Fund, managed bySSA, contains information regarding benefitcomputation and actions related to employeeentitlement. SSA routinely prepares reports re-garding specific disease entities and has pub-lished characteristics of workers disabled bycancer (283).

Exposure Data

The principal data deficiencies for assessingcancer risks are inadequate information aboutexposures and lifestyle characteristics. Sincecancer has a long latent period, relating cancerin today’s population to particular exposuresmight require information from 20 or moreyears ago. Even when information was col-lected, records may have been destroyed beforethey became useful in cancer epidemiologystudies.

As the lead agency for regulating chemicals,EPA administers numerous exposure-monitor-ing programs. Several studies have been criticalof EPA’s monitoring data collection efforts, andas a result, EPA established a Deputy AssistantAdministrators Committee to review and makerecommendations regarding agency monitoringand information management activities (113).Three of the major conclusions found by thecommittee are:

1.

2.

3.

A considerable quantity of collected ambi-ent environmental information has notbeen analyzed or presented to top man-agement.

The most serious problem found was thelack of consistent, integrated informationon toxic and hazardous pollutants.

There is little coordination between EPAoffices focusing on the same area. In addi-tion, there is a lack of comparability andsharing of these data.


Exposure data in the workplace are limitedeven though a number of cancer causing agentshave been identified in the occupational envi-ronment. NIOSH’s National Occupational Haz-ard Survey collects exposure data in a sample ofindustries, and OSHA requires monitoring for 6of the 20 substances regulated because of car-cinogenicity.

Death certificates generally include questionson the usual occupation and industry or busi-ness of the decedent, However, those questionsare not always answered and there is uncertain-ty about the accuracy of the information that isprovided. NCHS, along with NIOSH, is cur-rently assessing the feasibility of using and im-proving occupational descriptors on death cer-tificates as a surrogate for exposure infor-mation. Approximately a dozen States nowcode the usual occupation of the decedent, andabout half of these also code the reported usualindustry or business of the decedent. One State,Wisconsin, now publishes such tabulated infor-mation in their annual public health report.Other States, with support from NIOSH, haveexecuted special studies on occupational mor-tality based on data reported on the standarddeath certificate (45,236).

In England, information reported on thedeath certificate has been used as a basis for oc-cupational mortality analyses every 10 yearssince 1851 (with the exception of the war year,1941). In the United States, a study of this typewas conducted in 1950. It involved coding over300,000 death certificates for the occupationand industry of males aged 20 to 64. The in-formation was used in conjunction with the de-cennial census information for that year to pro-duce measures of relative mortality risk associ-ated with occupation and industry of decedents(148,149,150,151,196).

The National Human Adipose Tissue Moni-toring Program and HIS and HANES, which aredescribed above, are the principal mechanismsfor monitoring levels of toxics in the body. Thisinformation is used not only to determine nor-mal baseline levels but also to identify popula-tions which may beat high risk.

This assessment did not concentrate on moni-toring methods and programs, but the generalimpression is that data collection efforts are in-complete and that many generate data of limitedusefulness. For instance, measurement tech-niques are not always specified for collected ex-posure data and ignorance of the sensitivity ofthe instrument used makes it difficult to com-pare measurements from different times andsites. Furthermore, a nondetectable measure-ment does not necessarily indicate that a sub-stance is not present, and may mean only thatthe instrument was not sufficiently sensitive tomeasure it. Such negative readings are often notreported, and when they are, they may be mis-leading. The efforts of organizations such as theEPA Committee (113) mentioned above to im-prove collection and analysis of monitoringdata might be encouraged.

Chemical Information Systems

The lack of toxicological information aboutmany substances and concern over perceivedtoxic substance problems prompted Congress toenact more than two dozen statutes dealing withtoxics. Many of the statutes delegate informa-tion-gathering functions to Federal regulatoryand research agencies.

Toxic Substances Control Act —TSCA

In 1976, Congress passed TSCA to strengthenthe ability of the Federal Government to ac-cumulate information on potentially hazardouschemicals and better enable the Federal Govern-ment to protect the public from toxic sub-stances. TSCA required the establishment ofseveral new programs at EPA and a completelynew infrastructure had to be organized. Thisnecessitated recruiting an Assistant Admin-istrator and placed a large burden on a smallstaff. Subsequently, the programs have beenslow to get off the ground (141). Recruitmenthas continually lagged behind authorized staffceilings which may be inadequate to meet ex-pected program needs. EPA estimated that ap-proximately 1,500 people were needed in fiscalyear 1979: 382 permanent positions were au-thorized, 313 were actually filled.


New Chemicals. —One of TSCA’s primaryobjectives—as stated in the opening paragraphof the Committee on Interstate and ForeignCommerce Report (165), is to provide “for theevaluation of the hazard-causing potential ofnew chemicals before commercial productionbegins.” TSCA requires manufacturers and im-porters to notify EPA at least 90 days prior tothe manufacture or import of a new chemicalsubstance by submitting a premanufacture no-tice (PMN). Along with notification, manufac-turers are to provide specific information aboutthe new chemical, including any test data whichrelate to the effects of the substance on humanhealth or the environment. “New” is synony-mous with not being listed on the inventory ofexisting chemicals and subject to TSCA’s au-thority. In May 1979, EPA (105) issued a state-ment of interim policy covering submission andreview of PMNs. Final PMN rules have yet to beissued. In the 2-year period, April 1979 toMarch 12, 1981, EPA received 488 PMNs, andabout 800 are anticipated in fiscal year 1982.

TSCA was not the first Federal law to requirea review of new chemicals entering the market.FIFRA and the Food, Drug, and Cosmetics Act,have registration/certification provisions forpesticides and pharmaceuticals respectively.Unlike those laws, TSCA requires neither li-censing nor registration, but only notification ofintent to manufacture. As mentioned, the PMNmust contain any test data available to the sub-mitter, but EPA cannot require testing of a newchemical substance just because it is “new. ” Theact places the burden of proof on EPA to dem-onstrate that the information available to EPA:

. . . is insufficient to permit a reasoned evalua-tion of the health and environmental effects of achemical substance . . . and . . . [that] in theabsence of sufficient information . . . [the sub-stance] may present an unreasonable risk or willbe produced in substantial quantities, and theremay be significant or substantial exposure.

If such a finding is made, EPA may issue anorder under section 5(e) to prohibit or limit themanufacture, processing, distribution, use, ordisposal of the chemical. EPA has proposed twosuch orders and each time the company with-drew its notice and decided not to manufacture.

On two other occasions notices were withdrawnwhen the companies learned orders to requiremore information were in preparation.

Lack of regulatory action on a new chemicalby EPA does not imply that the substance is“safe” or has been “approved. ” However, it doesgrant the manufacturer the right to produce anduse the chemical as desired, subject to any otherregulations that may be applicable. Under sec-tion 5(a)(2) EPA can issue a “significant new userule” (SNUR) for a chemical when there is con-cern that a specific use of the substance, otherthan those proposed in the PMN, may pose anunreasonable risk. Issuance of an SNUR re-quires that persons must notify EPA 90 daysprior to manufacture or processing of a sub-stance for a use subject to a SNUR. ThroughMarch 1981, one chemical specific SNUR hadbeen proposed and EPA was considering SNURson more than 40 chemicals. Once a substance isin production, EPA can require testing underTSCA section 4 and/or submission of humanhealth and environmental monitoring data un-der a TSCA section 8 rule (see Existing Chem-icals).

EPA recently published a policy statement de-scribing a recommended list of premanufacturetests for new chemical substances (114). Thetests are identical to those under considerationby the Organization for Economic Cooperationand Development (OECD). OECD considersthat its base set of tests would generate theminimum amount of information normally suf-ficient to perform an initial hazard assessmentof a chemical (see table 31). EPA is recommend-ing that flexibility be used by manufacturers totailor this “base set” of tests for the particularchemical substance and intended uses. Use ofthis base set is voluntary due to EPA’s lack ofstatutory authority to require testing of newchemical substances. The estimated costs of thisbase set, should all tests be employed, rangefrom $53,000 to $67,850.

EPA has reported that no toxicity data weresubmitted in 60 percent of the first 199 noticesreceived (141). In fact, 25 percent of the noticescontained no data on physical or chemical prop-erties. No chronic test data have yet to be


Table 31.—EPA’s Recommended Base Set of DataTo Be Included in Premanufacturing Notices

Type of data Estimated cost

Physical/chemical dataData about 11 characteristics . . . . . . . . $ 3,800

Acute toxicity dataAcute oral toxicity. . . . . . . . . . . . . . . . . . 2,000Acute dermal toxicity . . . . . . . . . . . . . . . 2,800Acute inhalation toxicity . . . . . . . . . . . . - 3,300Skin irritation. . . . . . . . . . . . . . . . . . . . . . 700Skin sensitization . . . . . . . . . . . . . . . . . . 3,200-6,700Eye irritation (for chemicals showingno skin irritation). . . . . ., . . . . . . . . . . . 450

Repeated dose toxicity data14-28 day-repeated dose test(s) usingprobable route(s) of human exposure. . 10,200-12,800

Mutagenicity dataGene (point) mutation data . . . . . . . . . . 1,350Chromosomal aberration data . . . . . . . 18,000

Ecotoxicity dataData about killing of three lowerorganisms . , . . . . . . . . . . . . . . . . . . . . . . 4,100

Degradation/accumulation data . . . . . . . . 3,100-11,850SOURCE Office of Technology Assessment, adapted from EPA (I 14)

presented to EPA in a PMN. In cases where tox-icity data are given they are usually limited. Thethen-Assistant Administrator for Toxic Sub-stances has indicated (192) that the lack of testdata:

has placed an extraordinary burden on. . .EPA’s limited resources . . . . Furthermore, we[EPA] believe that our objective will not beachieved until industry assumes more of theburden of generating adequate risk informationand assessing the risk of its products.

Unless additional information is received withthe notices, EPA’s reviews will be “based upon afundamental lack of information and data. Thisin turn means that our information will be high-ly uncertain” (192). In order to evaluate a chem-ical’s carcinogenic potential, EPA staff have hadto rely on structure activity relationships andmutagenicity data when available.

Existing Chemicals, –Sections 4 and 8 ofTSCA relate directly to the issue of acquiringadequate information for assessing the carcino-genic risk of existing chemicals.

Section 4 grants EPA the authority to requireindustry testing of a potentially harmful chem-ical if available information is insufficient for a

reasoned evaluation of risk and if the substance:1) may present an unreasonable risk or 2) resultin substantial or significant exposure. TSCA es-tablished ITC to recommend chemicals for test-ing under section 4; ITC and EPA responses to itare described above. To require industry test-ing, EPA must demonstrate that available in-formation is insufficient to conclude that thesubstance “presents an unreasonable risk, ” yetsupports the finding that the chemical “may pre-sent an unreasonable risk. ” If available informa-tion were sufficient to show that the chemicalpresents an unreasonable risk, EPA could reg-ulate the substance under section 6 of TSCA.One difficulty EPA faces in using this testing au-thority is how to define “may present an unrea-sonable risk. ”

Section 8 of TSCA required EPA to compileby November 1977 an inventory of chemicalsubstances manufactured in the United States.An initial inventory was published about 2-1/2years late in June 1979 and updated in July 1980.Information originally requested for the in-ventory was limited and EPA has proposedrules requiring additional information for cer-tain substances. In February 1980, rules re-quiring exposure information on approximately2,300 substances were proposed (108). Addi-tional information-gathering rules are scheduledfor proposal in 1981.

Section 8(c) of TSCA also requires manu-facturers, processors, and distributors to notifyEPA of information which reasonably supportsthe conclusion that a substance “presents a sub-stantial risk” of injury to health or the environ-ment. In addition, Section 8(c) requires themaintenance of records indicating “significantadverse reactions” alleged to have been causedby a chemical substance. Allegation by employ-ees are to be retained by industry for 30 yearsand all other allegations for 5 years. These rec-ords are to be submitted to EPA upon request,and EPA is investigating means of establishingan automatic reporting system whenever a cer-tain number of allegations are received in a 12-month period for the same substance, process,or discharge (109). Final rules to implement thesignificant adverse reaction reporting require-ment are expected in 1981.


Chemical Substances InformationNetwork (CSIN)

In February 1978, under mandate of TSCA,EPA and CEQ established the Toxic SubstancesStrategy Committee (TSSC) to facilitate inter-agency coordination of chemical informationcollection, dissemination, and classification.The Departments of Health and Human Serv-ices, Agriculture, Commerce, Defense, Energy,Interior, State, and Transportation, and OSHA,CPSC, and NSF participate in TSSC. IRLG andthe DHHS Committee to Coordinate Environ-mental and Related Programs are also members.TSSC has formed a number of committees forspecial tasks, and the data committee recom-mended the development of a broad-based net-work of data systems—CSIN. CSIN wasadopted by TSSC, and if sufficient resourcesand personnel are committed, it should go along way toward the goal of providing conveni-ent access to information about chemicals. Itsmaster file will contain all information collectedunder TSCA; a subfile, stripped of confidentialdata about trade secrets, will be available forpublic use. CSIN will identify about 1 millionchemicals and for each one provide selected re-search and test data, references in the tox-icologic and biomedical literature, and in-formation about regulations that pertain to thechemical (345). The system is still in the devel-opmental stages, although some aspects wereexpected to be operational in 1980 and the entiresystem is to be completed within a decade.

CSIN will not be a single new system; ratherit will incorporate several systems already inuse. To facilitate locating information about asingle substance in more than one system, EPAis developing an unambiguous identificationnumber system, which was another recommen-dation of TSSC’s data committee. In this way,information about structure, chemical andphysical properties, production volume, uses,application, distribution, and toxicity, nowstored in different systems, can be linkedtogether. Such systems do not necessarily con-tain information about human health effects,but they can be used in combination with healthinformation systems.

Collection and Coordination ofExposure and Health Data

Congress has responded to concern about thecollection and availability of data for assessingenvironmental health risks. It has mandatedcommissions and studies directed at improvingdata collection, storage, and dissemination.

The Health Services Research, Health Statis-tics, and Medical Libraries Act of 1974, PublicLaw 93-353, mandated the U.S. National Com-mittee on Vital and Health Statistics to assistand advise PHS with statistical problems bear-ing on health and the delivery of health serviceswhich are of national interest. A committee rec-ommendation was important to the establish-ment of the NDI.

The 95th Congress passed two acts which in-cluded sections pertaining to data collection forassessing and reducing cancer risks. The CleanAir Act Amendments of 1977 (Public Law95-95) established the Task Force on Environ-mental Cancer and Heart and Lung Disease, tofocus efforts by EPA and various branches ofDHHS on issues relating to these diseases. Thetask force is composed of representatives fromEPA, NCI, NHLBI, NIOSH, NIEHS, NCHS,CDC, and FDA (340). The task force was di-rected to recommend, among other things (340):

. . . a comprehensive research program to deter-mine and quantify the relationships between en-vironmental pollution and human cancer . . .[and] . . . recommend research and such othermeasures as may be appropriate to prevent orreduce the incidence of environmentally relatedcancer . . . .

Initial efforts were focused on defining prob-lems, categorizing relevant research programs,and exchanging information among memberagencies and other appropriate groups. Activ-ities related to prevention and reduction of envi-ronmental risks are planned to begin during1981. ,

The task force established several projectgroups to address specific areas of interest. Ofparticular relevance to this assessment is theProject Group on Exposure and Metabolic

150 . Technologies for Detemining Cancer Risks From the Environment

Mechanisms, established in May 1979. Thegroup is examining the interrelationship of ex-posure to a toxicant and body uptake, metabo-lism, and affected target organs. It is hoped thatthis information will increase the ability of re-searchers to predict a chemical’s potential toxici-ty and establish which symptoms maybe associ-ated with trace chemical levels in the body.

The Project Group on Standardization ofMeasurements and Tests is primarily concernedwith obtaining reliable, comparable data on en-vironmental and disease measurements. Thegroup has focused on “potential contributions tothe state of the art of environmental and oc-cupational monitoring and testing that wouldcomplement, rather than duplicate or overlap,the efforts of individuals or agencies” (340).They identified two problem areas common totask force agencies:

1. There is a need for better resource alloca-tion to optimize the quality of data sinceagencies and laboratories charged withmonitoring activities typically have lim-ited resources.

2. Researchers currently have limited meansof assessing the relationship and validityof published environmental monitoringdata.

The Project Group on Standardization of Meas-urements and Tests expects to develop recom-mendations in these areas.

The Health Services Research, Health Sta-tistics, and Health Care Technology Act of 1978(Public Law 95-623) mandated the Secretary ofDHHS to initiate several efforts relating to theimpact of the environment on health. He is todevelop a plan for the collection and coordina-tion of statistical and epidemiological data onthe effects of the environment on health andprepare guidelines for the collection, compila-tion, analysis, publication, and distribution ofthis information. The law also authorized theSecretary of DHHS to “consult with and take in-to consideration any recommendations of theTask Force” in developing the plan.

NCHS (252) recently published Environmen-tal Health: A Plan for Collecting and Coordi-

nating Statistical and Epidemiologic Data,which reviews information currently availablefrom Federal data collection systems. A series ofrecommendations are made to Congress for cor-recting gaps and deficiencies in environmentalhealth data systems. These recommendationsinclude the need for priority setting in new datacollection efforts, interagency coordination inthe environmental data collection process,assurance of the quality of data, and linkingdata on the environment and health.

NCHS (252) identified 64 ongoing systems in18 agencies that gather environmental health-related data. At least two-thirds of these collecteither information on cancer incidence/mortali-ty or data on cancer risk factors. Most of thedata collection systems identified are designedto:

● collect health-related data,

● measure environmental pollutants and in-dividual exposures,

● test specific interrelationships, or● link data on the environment and health.

Linking systems that collect different kinds ofdata appear to have the greatest utility for as-sessing associations of environment and health.For example, the Upgrade system, which is con-cerned with water quality and health is a jointeffort of CEQ, EPA, NIOSH, and NCHS, andintegrates data from the Bureau of the Census,mortality data from NCHS, and water qualitydata from EPA and the U.S. Geological Survey.

OTA encountered an example of the often-voiced complaint that data are not in a formeasily accessible and useful to researchers. Na-tional mortality data were necessary to carry

out the analyses reported in chapter 2, but thosedata were available in computer readable formonly for the years since 1968. OTA had to com-puterize the data back to 1933 to carry out theanalyses. The OTA computer tapes of cancermortality data will be made available to re-searchers. These data include deaths by age,race, and sex for selected cancers, for each of theyears 1933 through 1978. All of the data onthese tapes are consistent with those availableon paper from NCHS.

Ch. 4—Methods for Determining and ldentifying Carcinogens 151

Not all informational systems release data forpublic use and some that are released are oflimited usefulness. Data are often aggregated bygeographical regions (e.g., by county or State),which precludes detailed analysis of exposureson health. Individual identifiers are frequentlydeleted because of privacy and confidentialityconstraints. This unfortunately hinders inten-sive specific epidemiologic investigations whichare facilitated by matching an individual’s ex-posures and lifestyle characteristics with healthstatus. Agencies with individually identifiedrecords can sometimes conduct followup studiesto obtain additional information for investiga-tion, e.g., NCHS recently initiated a followupstudy, 10 years after the survey, of participantsin its HANES I survey, The followup will inves-tigate current health status of participants as itcan be related to previously collected data.

Collection of useful epidemiologic informa-tion may be indirectly affected by the Paper-work Reduction Act of 1980, which passed dur-ing the last days of the 96th Congress. The act isintended to improve use of existing data collec-tion systems and to reduce the Federal paper-work burden placed on individuals, businessesand governments by 25 percent within 3 years.The act empowers the Director of OMB to re-view and approve Federal agency informationcollection requests. Various medical and epi-demiologic research groups, including NIH, ex-pressed concern that Federal research into dis-ease prevention could be impeded by the Paper-work Reduction Act and advocated the exemp-tion of biomedical and epidemiologic research(64), The Senate Committee on GovernmentalAffairs decided against this exemption becauseit determined that the act would not interferewith disease prevention research.

In addition to reducing the paperwork bur-den, the act directs the sharing of informationamong agencies to the extent authorized by lawand the establishment of a Federal InformationLocator System. This system will contain a de-scription of all information collected by the Fed-eral Government, and directions for obtainingthe information by all agencies and the public.Successful implementation of this system should

enhance the quality of information available forepidemiologic research.

Government Records andRecord Linkage

Government records contain a wealth of in-formation about individuals that could be ofgreat value to researchers looking for associa-tions between exposures and disease states. TheSSA, Internal Revenue Service (IRS), Veterans’Administration (VA), the Bureau of the Census,and NCHS are organizations with extensivedata collections. For the most part, details aboutindividuals are not readily available because oflegal and institutional barriers. Most critically,it is difficult to obtain records of the same per-son from two or more sources. This can be amajor obstacle because one record rarely con-tains all desired information. For example, to doa study relating mortality to occupational ex-posures, one could extract “occupation” fromthe IRS record, “employer” and “industry” frominformation collected by the SSA, and cause ofdeath from the death certificate filed in the Statein which the death occurred. The NDI, which isdescribed above, makes it easier to locate deathcertificates.

Individuals in several Government agencieshave been promoting a Linked AdministrativeStatistical Sample, a project designed to bringtogether records of IRS, SSA, and NCHS (200).The project planners aim to provide an improv-ed data base for mortality research by compilingstatistical information from the participatingagencies on a sample of individuals. The start-ing point will be the l-percent CWHS (seeabove). This effort has great importance as apilot for future projects to study cancer mortal-ity, particularly contributions of occupationalexposures.

Records from different agencies have beenlinked before on an ad hoc basis, e.g., VA hascooperated in several studies (23), but thebroader scale now proposed has brought somebasic issues to the fore. The most fundamentalbarrier to researchers acquiring data from morethan one file is that which is erected to preserve

privacy and confidentiality. Restrictions havebeen tightened considerably in recent years bythe Privacy Act of 1974 and the 1976 amend-ments to the Internal Revenue Code. Althoughepidemiologists have not been implicated, well-publicized breaches of confidentiality and pri-vacy have engendered suspicion among legisla-tors and the public, about possible misuse ofeasily accessible files. MacMahon (217) hassummarized the epidemiologist’s point of view:

To determine cancer risks among persons ex-posed to particular environmental factors, weneed to be able to link information relating tothe same individual at different times in his lifeand to determine whether an individual exposedin the past is now dead or alive and in what stateof health . . . . Maximum confidentiality meansminimum epidemiologic information and min-imal effectiveness in identifying new cancerhazards. In my opinion, we are well beyond thepoint at which concern for confidentialityseriously impairs the extraction of valuableknowledge, even from routinely collected in-formation. Working as an epidemiologist, onecomes to recognize the readiness with whichmost people, patients or nonpatients, will sup-ply even sensitive information if they believe thecause is reasonable. Somehow, the issue of con-fidentiality becomes more difficult when it isinstitutionalized or politicized. We must attemptto convince the public’s representatives that areasonable balance can be achieved.

Other linkages, and the means to accomplishthem, have been suggested. One current pro-posal involves drawing a sample of several mil-lion individuals from those people who filledout the 1980 long census form for future match-

SUMMARY

Interest in cancer prevention and acceptanceof the idea that some substances cause cancerhave spurred developments in methods to deter-mine which substances are associated withcancer.

Epidemiology has played an important role inidentifying both carcinogenic substances and ex-posures which are associated with cancer al-though the causative agent may not be known.

ing to the NDI. This would facilitate matchingcause of death with personal characteristicsreported in the census. Another proposal hasbeen made to add cause of death information tothe SSA’s l-percent CWHS. However, since col-lection of cause of death data is not part of themission of SSA, it would presumably requiremoney from outside SSA for implementation.

The cited desirability of making records moreavailable for research purposes runs into con-flicts with society’s intention of protecting theindividual’s privacy. The linking of individualrecords between agencies would allow a personwith access to the system to obtain most or allGovernment-held information about any indi-vidual. The potential for abuse is apparent. Atthe same time, linkage, in the hands of a bio-medical researcher, might quickly provide in-formation about behaviors, exposures, andhealth that could be obtained only with greatdifficulty in any other system.

The Workgroup on Records and Privacy ofthe Interagency Task Force on the Health Effectsof Ionizing Radiation (182a) has addressed theproblems arising from the conflict between ac-cess to records for research and the right toprivacy. It suggested changes in the PrivacyAct, the Tax Reform Act, and commented onpending bills (in 1979) that would have per-mitted access to records under tightly controlledconditions. The workgroup’s report is an excel-lent starting point for discussion of this com-plicated subject and provides possible directionsfor, Federal efforts.

When available, epidemiologic data about can-cer risks are the most convincing. At the sametime, identifying a carcinogen on the basis ofhuman disease and death means that other test-ing methods failed to identify the agent beforehuman illness resulted from it.

The most important laboratory method fordetermining carcinogencit y is the long-term bio-assay in laboratory animals, generally rats and

mice. The 1960’s saw marked increased interestin the test, and NCI has played a major role indesigning appropriate test methods. NCI devel-oped a large-scale bioassay program for testing,evaluating, and documenting the carcinoge-nicity of environmental chemicals. It has alsosupported the IARC program to review infor-mation on environmental carcinogens and pub-lish findings in its authoritative monographseries.

While the bioassay has been improved and iswidely accepted as an appropriate method toidentify carcinogens, it is expensive (each onecosts $400,000 to $1 million) and time-con-suming (each takes from a minimum of morethan 2 years to a more realistic 5 years). Becauseof those costs and limited long-term bioassaycapacity, other tests are being developed.

The short-term tests measure biological ef-fects other than carcinogenicity (often mutagen-icity) in bacteria, yeast, cultured mammaliancells, or in intact lower organisms. Major inter-national efforts have been completed and othersare ongoing to validate the ability of these teststo identify correctly carcinogens and noncar-cinogens. Some tests perform well in the vali-dation experiments, and it is expected that theywill play an increasingly important role in iden-tifying carcinogens.

Deciding to test a chemical in a short-termtest or a long-term bioassay involves studyingits structure. Some classes of chemicals are morelikely to be carcinogenic than others, some arepresent in high concentrations in the environ-ment, and some are viewed with suspicion forone reason or another. Based on such informa-

tion a chemical may be selected for testing. NTPis developing a tier-testing scheme which firstassays a chemical in a number of short-termtests. The chemicals that appear most risky as aresult of short-term tests will be accorded priori-ty for further testing in long-term bioassays.This NTP program promises to improve boththe use of information from short-term tests andthe usefulness of the bioassay program.

The establishment of NTP, which appears tobe moving toward an ordered, careful devel-opment of methods for testing and interpreta-tion of results, and IRLG’s appearing as a singlevoice for Federal regulatory procedures anddecisions promise further improvements. Addi-tionally, IARC’s distinguishing between non-carcinogens and carcinogens and orderingamong carcinogens on the basis of test results isan important step in increasing the usefulness ofthe results.

Not included in testing systems, but discussedhere are already useful and potentially moreuseful data collection systems. Several of thesesystems were mandated by Congress to collectinformation about exposures and health status.Currently, inadequate resources and coordina-tion may be hampering the performance of thesystems. Another major source of information,the administrative data systems, were not de-veloped as health information resources. How-ever, both SSA and IRS collect some informa-tion which might be of great value for epidemi-ologic studies. Perhaps the most pressing needin adapting the administrative data systems forthese uses is more consultation between epide-miologists and the data systems experts.

methods for detecting and identifying carcinogens

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