[CANCER RESEARCH 34, 3026-3039, November 1974]

of epithelium around segmental bifurcations (13, 14).Recently, Martell (17) has shown that 210Pb (parent isotopeof 210Po) is present in tobacco smoke in the form of veryhigh specific activity “hot―particles which may penetratethe bronchial epithelium and lead to the accumulation ofhigh local concentrations of 210Po. Although the radiationdose from 210Po in the epithelium of smokers is not of themagnitude usually associated with the production of lungtumors in experimental animals, it might be highly significant if a-radiation acted synergistically with the knownchemical carcinogens in cigarette smoke. For these reasons,we have been developing a small animal model for theinduction of lung cancer by chemical carcinogens anda-radiation, so that we may eventually study the interactions between the 2 types of agents.

The Syrian golden hamster was chosen for this studybecause it has been shown to be very resistant to pulmonaryinfections (4, 6), to develop rarely spontaneous lung tumors(4, 19), and to develop a high incidence of lung cancerwithout marked inflammatory changes following intratracheal instillation of polycyclic hydrocarbons adsorbed oncarrier particles (19). Prior attempts to induce lung cancerin mice or rats by a-radiation have generally yielded a verylow incidence of tumors, unless very high radiation doseswhich led to extensive inflammatory changes and fibrosiswere used (9, 22). Furthermore, these rodents are prone todevelop chronic endemic pulmonary infections.

This report is designed to describe the incidence andhistopathology of respiratory tract tumors induced inSyrian hamsters by multiple intratracheal instillations ofeither 210Po or BP2 adsorbed onto hematite carrier particles.In preliminary reports, data have previously been presentedon the occurrence of lung tumors following exposure toeither carcinogen ( I 1), as well as on the role of the carrierparticles in 210Po carcinogenesis (12).

MATERIALS AND METHODS

Animals. Syrian golden hamsters of both sexes approximately 8 weeks old and weighing 100 to 125 g were obtainedfrom Dennen Animal Industries, Gloucester, Mass. Theywere housed 3 or 4 to a cage in an environment-controlledroom maintained at 25°with a 12-hr light-dark cycle. Theywere fed Purina laboratory chow and given tap water adlibitum. Intratracheal instillations were begun when theanimals reached I 1 weeks of age.

2 The abbreviation used is: BP, benzo(a)pyrene.

3026 CANCER RESEARCH VOL.34

Respiratory Tract Tumors in Hamsters Induced by Benzo(a)pyreneand 210Po a@Radiation'

JohnB. Little andWilliamF. O'TooleDepartment of Physiology, Harvard University School of Public Health, Boston, Massachusetts 02! 15

SUMMARY

A high incidence of respiratory cancer has been inducedin Syrian golden hamsters by repeated intratracheal instillations of either benzo(a)pyrene or 210Po adsorbed ontohematite carrier particles. Both the tumor incidence and themean induction time were related to the dose of carcinogen.Benzo(a)pyrene induced a spectrum of tumors, amongwhich, the types occurring most frequently were epidermoidcarcinomas of the trachea or major bronchi. 210Po-inducedtumors were almost exclusively combined epidermoid andadenocarcinomas that arose peripherally; these tumorsoccurred in 94% of animals in the highest exposure group.Hamsters appear particularly susceptible to the induction oflung cancer by a-radiation at doses that do not produceconcomitant lung damage, and they may provide a goodmodel for the study of interactions between radiation andchemical agents in respiratory carcinogenesis.

INTRODUCTION

a-radiation has been implicated as the cause of the veryhigh mortality rate from lung cancer found in several groupsof underground mine workers exposed to radon daughterproducts in the air of the mines (1). It has been estimatedthat 40 to 80% of the deaths among the miners inJoachimsthal and Schneeberg in central Europe resultedfrom radiation-induced lung cancer (I, 15). More recently,a-radiation has been associated with the increased lungcancer incidence among the Newfoundland fluorspar miners(5), the West Cumberland hematite miners (2), and theColorado Plateau uranium miners (24). The findings withrespect to the Colorado miners are of particular interest inthat the high incidence of lung cancer is almost entirelyassociated with the group of miners who are also cigarettesmokers (16), suggesting that a synergistic effect may existbetween cigarette smoke and a-radiation in the induction oflung cancer.

Cigarette smoke itself contains small amounts of thea-emitting radionuclide 210Po (18), and 210Po has beenshown to accumulate in the bronchial epithelium of cigarette smokers (14). Average smokers may receive radiationdoses of 8 rem/year or more from this source to small areas

I Supported by Grant P-613 from The American Cancer Society, Grant

I345-C- 1 from The American Cancer Society (Massachusetts Division),and Grant ES-00002 from the NIH.

Received April 15, 1974; accepted August 7, 1974.

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

No.bearingTreat

mentgroupCarcinogenoDose! instillationNo.

ofanimals

autopsiedbrespiratory

tumorsTumorincidence1Control;

noinstillations60002Control;hematiteonly34003210Po0.2@iCi353497%4‘10PoO.2zCic372568%5“°Po0.01

@Ci321753%6Benzo(a)pyrene3mg392462%7Benzo(a)pyrene0.3

mg3738%

Induction of Lung Cancer by BP and a-Radiation

weekly instillations each of 3 mg BP vith 3 mg hematite,and Group 7 received 15 instillations of 0.3 mg BP with 3mg hematite.

RESULTS

Tumor Incidence and Induction Time. Tumor incidencedata for control groups and for hamsters treated with 210Poor BP are shown in Table I . No tumors occurred in either ofthe control groups, whereas the overall tumor incidenceappears related to dose for both 210Po and BP. For 210Po, asignificant relationship between radiation dose and tumorinduction time was also present. Data for Groups 3 and 5are plotted in Chart I . The mean induction time was ISweeks longer for the low-dose group, and 60% of theanimals in Group 3 had died with lung tumors before the 1sttumor was found in Group S.

The apparent effect of dose on the overall tumor mcidence as shown in Table 1 could have been due primarily tothe effect on induction time; if induction time was sufficiently prolonged at the lower doses, animals would begin todie of other.causes before they developed tumors. Ifthis wasindeed the case, one would expect the earlier deaths in thelow-dose groups to be due to other causes, whereas the latedeaths should be primarily due to tumors. To test thishypothesis, we have correlated the time of death with thepresence or absence of lung tumors for the 2 lower-dosegroups. (For the high-dose group, all but I hamster diedwith tumors.) These results are plotted in Chart 2. Deathswithout lung cancer occurred ar random throughout theposttreatment period. If anything, the later deaths includeda preponderance of tumor-free animals. These resultssuggest that radiation dose has a specific effect on tumorincidence as well as on induction time.

Data on the induction time for tracheal tumors found inBP-treated hamsters in Group 6 are shown in Chart 3.Epidermoid carcinomas and spindle-cell tumors have beenplotted separately, as the induction times for these tumorsappeared quite different. The induction times for all types of

Carcinogen Suspensions. Hematite carrier particles(Fe203) were obtained from the Fisher Scientific Co., FairLawn, N. J.; 98% of them had a mean diameter of less than0.75 sm as determined by electron microscopic sizing of thedry powder (I 1). BP was obtained from the AldrichChemical Co., Milwaukee, Wis. BP was adsorbed onto thehematite particles by grinding them together by the methoddescribed by Saffiotti et a!. (19). 210Po, which emits a 5.3MeV a-particle with a track length of 37@sm,wasobtained asa carrier-free Po(N03)4 solution in 1.0 N HNO3 from NewEngland Nuclear, Boston, Mass. 210Po was adsorbed ontohematite particles by adding 210Po in a very dilute HNO3solution to a 0.9% NaCI solution suspension of the particlesand incubating the mixture for 24 hr at 4°(polonium bindsreadily to surfaces).

Procedures. The particles to which carcinogens wereabsorbed were suspended in 0.9% NaCI solution, and thesuspension was treated sonically for 15 mm, then wastransferred to a magnetic stirrer for the duration of a courseof instillations. In all experimental groups, 0.2 ml of 0.9%NaCl solution suspension containing 3 mg of hematiteparticles was instilled into the tracheas of hamsters lightlyanesthetized with sodium brevital (Eli Lilly and Co.,Indianapolis, md.). The animals were observed for theirnormal lifetimes, and allowed to die spontaneously or weresacrificed when moribund. The inflated lungs and tracheawere removed together, fixed in alcohol-formalin fixative,and embedded in paraffin blocks. Sections 8 @tmthick werecut and stained- with either hematoxylin and eosin orperiodic acid-Schiff for histopathological study. Pathological evaluations were made without knowledge of thetreatment group to which the animal belonged.

Treatment Groups. Animals were divided into 7 treatmentgroups (Table 1). Group I consisted of colony controlhamsters which were maintained simultaneously with otherexperimental groups but which received no treatment.Group 2 received 15 weekly instillations of 3 mg of hematitealone in 0.2 ml 0.9% NaCl solution. Groups 3, 4, and 5 allreceived 210Po on 3 mg of hematite. Group 6 received 15

Table ITumor incidence in hamsters given multiple intratracheal instillations of “°Poor BP

a All animals (except those in Group I) received 3 mg hematite particles suspended in 0.2 ml 0.9%

NaCI solution.b Including only animals that survived the treatment period.CThis group received 7 instillations. All other groups received 15 weekly instillations. The

approximate radiation dose to the whole lung, on the basis of preliminary radiochemical analyses,was 5000, 2000, and 300 rads, respectively, for the 3 210Pogroups.

NOVEMBER 1974 3027

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

00

(, 80z4LU0 60

0

I—

LU>

@ 20

SiteCarcinogenBenzo(a)pyrene‘10PoTracheaEpidermoid

carcinoma82Squamouscellpapilloma20CarcinomainsituI0Spindle-cell

tumor100LungEpidermoid

carcinoma(bronchus)42Combinedepidermoidand875adenocarcinoma

(peripheral)Small-cellanaplasticcarcinoma30Metastatic

carcinoma10Sarcoma(metastatic)01

50 60 70 80

J. B. Little and W. F. O'Toole

(4, 6, 19), moderate to marked chronic pulmonary inflammatory changes were present in most animals from both thecontrol and treatment groups. The changes were primarilyperibronchiolar, were associated with hematite deposits inthe treatment groups, and progressed with age. They werenot noticeably less marked among control (Group I)animals. Beyond these changes, subpleural emphysema,marked peribronchiolar fibrosis, or areas of necrosis werelate findings in about 5% of all animals in both the controland treatment groups, with the exception of Group 3(high-dose 210Po). One or more ofthese changes was seen in50% of Group 3 animals; emphysema was found in 16 of 35hamsters in this group. Fibrotic and inflammatory changesin the lower-radiation groups were no more marked than ineither of the control groups. Focal lung necrosis with acuteinflammatory changes was associated with several largecentral tumors.

‘Q__@O 30@ 50 60

TIME (WEEKS) AFTER I@ INSTILLATION

Chart 3. Induction time for tracheal tumors in BP-treated hamsters(Group 6). Horizontal axis, time of death.

Table 2

i/Ic.... 5000rods (3)

.—.300rods (5)

0 0 20 30 40.4

Treatmentperiod TIME(WEEKS)AFTER FIRST INSTILLATION

Chart I. Influence of radiation dose on induction time for tumors induced by “°Po.These tumors were almost exclusively combined epidermoid and adenocarcinomasin the peripheral lung. Horizontal axis, timeof death.

10 20 30 4:0 @O @O 7:@@

TIME OF DEATH (WEEKS AFTER FIRST INSTILLATION)

Chart 2. Presence (+) or absence (0) of lung tumors at death in“°Po-treatedhamsters in Groups 4 and 5.

lung tumors found in BP-treated animals in Group 6(including epidermoid carcinomas) were similar to that forthe epidermoid carcinomas of the trachea (Chart 3). Twotumors in Group 7 (an epidermoid carcinoma of the tracheaand a combined epidermoid and adenocarcinoma of thelung) occurred at 60 and 103 weeks, respectively. This resultis consistent with that of Saffiotti et a!. (20, 2 1), who found asignificant lengthening of the latent period for BP-inducedrespiratory tumors with lower doses of BP. The 3rd tumorin Group 7 was an undifferentiated small-cell tumor foundat 64 weeks. Multiple tumor nodules were present in boththe lungs and the liver; the site of the primary lesion couldnot be definitely established.

Pathology. The distribution of tumors by histologicaltype is given in Table 2. The pathological material is on thebasis of a total of 76 hamsters that received 210Po and thatbore one or more respiratory tumors at the time of death,and on a total of 27 hamsters that were given BP and thatdied with tumors. In the absence of a standard classificationfor lung tumors in hamsters (7), we have used the WorldHealth Organization classification of human lung carcinoma (Table 3) as the basis for histological typing ofmalignant pulmonary lesions.

Inflammatory Changes. Contrary to the findings of others

60

40

20

( /N@LE CELL

TUMOR

0 -EPIDERMOIO

CARCINOMA

DOSEGROUP

(5)300rods

(4)2000rods

0-No tumor+-Lung tum@

0 @% + .*+@0 +4@@ + 00 0@ +

0 0@4@@ Of+ ++.s-.-s.+@+8 o+ @+ 0

Histopathology ofrespiratory tumors induced by “°Poor BP

Table 3World Health Organization Committee classification oflung carcinoma

1. Epidermoid carcinoma

ii. Small-cell anaplastic carcinomaiii. Adenocarcinomaiv. Giant-cell carcinomav. Combined epidermoid and adenocarcinoma

vi. Bronchiolar-alveolar carcinoma

3028 CANCER RESEARCH VOL.34

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

Induction ofLung Cancer by BP and a-Radiation

Tumor Location and Site of Origin. The BP-treatedanimals generally developed tumors of the large airways,i.e., the trachea, extrapulmonary bronchi, and segmentalbronchi. These animals showed a considerable degree ofbronchial epithelial hyperplasia, and these major airwaytumors appeared to originate from the pseudostratifiedcolumnar epithelium which had undergone squamous metaplasia and atypical hyperplasia.

The picture was very different, however, in the 210Potreated hamsters. These animals developed peripheral lungtumors almost exclusively, which were histologically cornbined epidermoid and adenocarcinomas. Bronchiolar epithelial hyperplasia was a prominent feature of nearly all210Po-treated hamsters. If the assumption is valid thatthere is a continuum between these peribronchiolar proliferations and the large lobar tumors classified as carcinomas,then the site of origin of these tumors appears to be thecuboidal epithelium of the terminal bronchioles.

Tracheal and Bronchial Epithelial Hyperplasia. Thesechanges are an increase in the number of cell layers of thelining of tracheal or bronchial epitheliurn with or withoutatypia and squamous rnetaplasia (Figs. 1 and 2). Data onhyperplasia of tracheal epitheliurn are presented in Chart 4.Except for 1 210Po-treated animal, tracheal epithelialhyperplasia was confined to the BP group. It was associatedwith moderate to marked squamous metaplasia in 16animals; 8 of these did not have tracheal tumors. In thebronchi, mild hyperplastic changes were seen in someanimals from all treatment groups, but the changes weremost severe in the larger bronchi of BP-treated hamsters.

Epidermoid Carcinoma. An example of an epidermoidcarcinoma of the trachea is shown in Fig. 3, and anepidermoid carcinoma of the lung is shown in Fig. 4.Tracheal carcinomas exhibited extensive invasion of thewall of the trachea, not only the lamina propria, but also thefull thickness of the wall. The anatomic site of origin ofepidermoid carcinomas was frequently difficult to identify,especially those tumors at the hilum of the lung near thetracheal bifurcation and those that were large and involvedboth the wall of the large bronchus and adjacent pulmonaryparenchyma. Most of the tracheal carcinomas in Table 2occurred near the bifurcation, and a number of them mayactually have arisen in a major bronchus.

The designation “epidermoidcarcinoma in situ―of thetrachea was used when the epithelial lining exhibited focalhyperplasia with disruption of the orderly stratification ofthe epithelium and individual cell atypia. An example of

@: :

I UUH 10 ,,@0 I@2@3@4@ 0 I@2@3@4@BENZOPYRENE POLONUM 0.2@iCi

Chart 4. Incidence of tracheal epithelial hyperplasia at death in BPtreated (Group 6) and “°Po-treated(Group 3) hamsters. Hyperplasiascored from 0 (none) to 4+ (severe) without the observer having foreknowledge as to which of the 7 treatment groups (Table I) the animal belonged.

epidermoid carcinoma in situ is shown in Fig. 1.Squamous Cell Papiloma. This designation was ap

plied to tumors with an exophytic growth pattern extendingfrom a narrow base into the lumen of the trachea or bronchus. It is covered by orderly stratified squamous epithehum or stratified squamous epithelium with slight tomoderate atypia. The supporting stroma of the tumor is ofdelicate, orderly connective tissue.

Spindle-Cell Tumors of the Trachea. This term has beenapplied to a group of tumors that differed in certaincharacteristics from the epidermoid carcinomas describedabove. They were invariably found within the trachea; thespecific segment of the trachea was not consistent. Ingeneral, they were exophytic, protruding into the lumen,and were often lobulated. Examples of these tumors areshown in Figs. S and 6. The luminal surface of the tumormass was generally lined by stratified squamous epithelium.This epithelium was often relatively normal in appearance,although there invariably were foci of hyperplasia withmarked atypia of the stratified squamous epithelium. Thenormal columnar epithelium was replaced by stratifiedsquamous epithelium in broad areas of the trachea in all ofthe tumor-bearing animals. The great bulk of the tumorvolume was made up of spindle-shaped stromal cells, oftenwith eosinophilic cytoplasm and an admixture of collagenstroma. In addition, however, there were large polygonaland irregularly outlined cells with poorly defined cellborders and giant nuclei with a highly atypical chromatinpattern (Fig. 5).

The question of whether these are true tumors or whetherthey merely represent inflammatory reaction with atypicalstromal reaction might be raised. The presence of atypicalstratified squamous epithelium with obvious epidermoidcarcinoma and transitional cells intermediate in appearancebetween the epidermoid carcinoma and the stromal tumorcells, the extensive invasive characteristics of these tumors,and the finding of metastasis to an adjacent lymph node in 1animal (Fig. 6c) argue conclusively, in our minds, for theclassification of these as true malignant neoplasms. It ischaracteristic of these tumors to penetrate deeply throughthe wall of the trachea though in its noncartilaginousportion, completely surround the cartilaginous plate, andinflitrate widely into the surrounding tissues.

On the other hand, these tumors may well representsimply an atypical or undifferentiated form of epidermoidcarcinoma. The designation “spindle-celltumor of thetrachea― implies that malignant epithelial cells from thestratified squamous epithelium become sufficiently undifferentiated so that they closely resemble the malignant cellsof a stromal sarcoma. Transitional forms between malignant-appearing epithelial cells and the malignant-appearingstromal cells have been demonstrated in some animals.Because of these histological features and because theinduction time for these tumors appeared to differ from thatfor epidermoid carcinoma (Chart 3), we have classifiedthem separately.

Bronchiolar Epithelial Hyperpla.sia. This was a prominentfinding in most of the 210Po-treated hamsters and wascharacterized by the appearance of cuboidal or columnarcells lining alveoli adjacent to small bronchioles. These foci

NOVEMBER 1974 3029

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

J. B. Littleand W. F. O'Toole

were readily identifiable as fairly discrete patches aroundmany bronchioles (Fig. 7). The cells usually exhibited nosignificant degree of atypia, although squamous metaplasiawas present in the more advanced lesions. Another consistent feature of these lesions was the apparent presence of theproliferative cells within preexisting alveolar spaces; that is,the underlying architecture of the alveoli was still generallydiscernible. Whereas marked bronchiolar epithelial hyperplasia was a common and early finding in most 210Potreated animals, it was much less severe in BP-treatedanimals. The distribution ofthese changes in Groups 1, 2, 5,and 6 (Table 1) are shown in Chart S. Areas of mildbronchiolar epithelial hyperplasia were observed in somecontrol animals (Chart 5), and marked changes were foundin 1 colony control hamster and in I hamster that receivedhematite alone. These hamsters died at 108 and 88 weeks,respectively, after the 1st instillation.

Combined Epidermoid and Adenocarcinoma of the Lung.Beyond these hyperplastic changes, which may be quiteextensive in an individual animal, there was a group of franktumors with many similar characteristics, namely, a papillary alveolar growth with many foci in which the epitheliumhad undergone focal squamous differentiation. These lesions often displayed little cellular atypia. The lesions thatwere designated as combined tumors were differentiatedfrom bronchiolar epithelial hyperplasia by the followinggeneral criteria. (a) Size, involvement of more than Ibronchiolar field or lobule. In many animals, this tumorinvolved entire lobes of lung from pleural surface to pleuralsurface (Fig. 8). (b) The presence of significant atypia,although not a constant feature, was present in a largenumber of these tumors. (c) Invasion of supporting stromaof the lung was a characteristic feature, indicating themalignant potential of this group of tumors. Foci of tumorinvaded the adventitia of large bronchi within connectivetissue septa and pleural surfaces (Figs. 9 and 10). (d) Thepresence of clear-cut blood-vessel invasion was demonstrated in some tumors (Fig. 9). Those animals in whichblood-vessel invasion was found were without questionproperly grouped with regard to the category of tumor.

0 t@2+3@4+

I€MATITECONTROLS

Chart 5. Incidenceof bronchiolarepithelialhyperplasiaat death in animals from Groups I, 2, 6, and 5. Hyperplasia scored from 0 (none) to 4+(severe) without the observer having foreknowledge as to which treatmentgroup the animal belonged.

Although a systematic search for blood-vessel invasion inevery tumor is not yet completed, it was present in a numberof animals.

Almost all of the pulmonary carcinomas induced by210P0, as well as a significant fraction of those induced byBP, were classified as combined carcinomas. These tumorswere frequently multicentric in origin and sometimes involved entire lobes even at relatively early times (Fig. 8).They were characterized by the presence of both adenomatous and epidermoid features in different fields of the sametumor (Figs. 10 and 11). Although either histology predominated and to different degrees, the adenomatous componentwas more frequent. Clear-cut invasive characteristics wereoften demonstrated in tumors whose histological featureswere otherwise relatively benign (Fig. 9). The tumors wereusually associated with widespread areas of bronchiolarepithelial hyperplasia; many of the 210Po-treated hamstersthat did not develop frank carcinomas showed these hyperplastic changes.

The relationship between the presence of combinedcarcinomas and other forms of pulmonary pathology is ofsome interest. A consistent pattern of fibrosis or chronicinflammation was not identifiable. A number of animals inGroup 3 did exhibit foci of fibrosis, especially around heavyconcentrations of hematite particles with occasionally entrapped nests of epithelial cells, resulting in foci that closelyresemble invasive tumor, and constituting a source ofpossible misinterpretation.

Small-Cell Anaplastic Carcinoma (UndifferentiatedCarcinoma). These tumors were composed of irregularnodules which were generally peripheral in location. Exampies of these tumors are shown in Fig. 12. Each nodule wasmonomorphic and composed of sheets and cords of denselypacked cells which were small with fairly regular round andoval nucleii. The scant cytoplasm was faintly basophilic andwithout a distinct cytoplasmic membrane. Connective tissuestroma was not a prominent feature. The tumor cordsappeared to be separated by a vascular channel which waslined by a single layer of endothelial cells

DISCUSSION

These results indicate that a high incidence of lungcancer can be induced in Syrian hamsters by either BP or210Po a-radiation. Although moderate chronic pulmonaryinflammatory changes were present in our hamster colony,tumor induction by BP or the lower doses of 210Po (Groups4 and 5) was not associated with the production of lungdamage such as extensive pneumonitis, necrosis, or interstitial fibrosis.

The histological types, anatomic location, and apparentsite of origin of the tumors induced by the 2 carcinogendiffered markedly. BP-induced tumors were primarily epidermoid carcinomas that were central in location, originating from the trachea and major bronchi. BP-treated hamsters exhibited extensive hyperplasia of the tracheal andbronchial epithelium, and only mild-to-moderate bronchiolar epithelial hyperplasia. 210Po-induced tumors were almost exclusively combined epidermoid and adenocar

C,)-j4

z4

LU

z

0 I@2@3@4@ 0 I@2@3@4@BENZOPYRENE POLOMUMQOI@Ci

3030 CANCER RESEARCH VOL.34

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

Induction ofLung Cancer by B? and a-Radiation

cinomas that arose peripherally. Marked bronchiolar epithelial hyperplasia was a characteristic finding in 210Potreated animals, whereas hyperplasia of the epithelium ofthe trachea and major bronchi was practically absent. Thesefindings suggest 2 possibilities; either the epithelial cells aredifferentially sensitive to the 2 carcinogens, or the carcinogens are reaching and acting at different sites in the lung.

Recent evidence suggests that the carcinogens do reachdifferent cell populations following administration on hematite carrier particles (8). Autoradiographic studies haveshown that 210Po is a firmly bound, insoluble carcinogenwhich remains associated with the visible hematite particlesin the lung (8, 12). As the hematite that is not rapidlycleared from the lung is deposited and retained primarily inthe region of the alveolar ducts (8), the major radiation dosefrom 210Po would be to the peripheral airways. On the otherhand, BP is a loosely bound soluble carcinogen that leavesthe carrier particles and enters upper airway epithelial cellsduring clearance of the particles on the mucous ciliaryescalator (8). Thus the tracheal and bronchial epitheliumreceive significant exposure to BP.

Although several animal lung-tumor classifications havebeen proposed (7), none to our knowledge is generallyaccepted. We have, therefore, adopted the classification oflung tumors as set forth by the World Health OrganizationCommittee (Table 3), in order not to introduce a new set ofterms at this time. The distribution and histological featuresof the tumors in our BP-treated animals are very similar tothose found by Saffiotti et al. in similarly treated hamsters(19—21).Squamous metaplasia and bronchial and trachealepithelial hyperplasia with and without atypia were frequentfindings in BP-treated hamsters [compare Saffiotti et al.(19), Figs. 7 and 8, with our Figs. 1 and 21. Typicalepidermoid carcinomas were also frequent in the BP-treatedgroup [compare Saffiotti et a!. (19), Figs. 13 and 16, withour Figs. 3 and 4]. We would also classify their Fig. 29 as apoorly differentiated epidermoid carcinoma. The differencein the relative distribution of epidermoid carcinomas between the bronchi and trachea in the 2 studies probably isrelated to how one assigns the origin of large tumors in thehilar region. Another difference is the large number ofspindle-cell tumors of the trachea in our study. Saffiotti etal. (19, 20) reported finding 2 carcinosarcomas, a tumorthat has the histological characteristics of our spindle-celltumors. These authors probably classified others of thesetumors as poorly differentiated epidermoid carcinomas.

Classification of peripheral lung tumors has proven moreproblematical. Small tumor nodules have been the mostdifficult to classify. Increased numbers of epithelial cellsconfined to a terminal bronchiole, its ducts and alveoli, andproliferating in an alveolar-papillary pattern have beenvariously interpreted by others as bronchiolar epithelialhyperplasia, adenomatoid lesions, and small adenomas, toname but a few terms. Our choice has been to classifyepithelial cell proliferation as hyperplasia if the growthpattern of the cells is confined to preexisting air-containingspaces. We would classify lesions such as those shown inFigs. 34 and 35 in the paper by Saffiotti el al. (19) asmarked bronchiolar epithelial hyperplasia (see our Fig. 7).

If, however, the pattern of proliferation is invasive in natureand at the expense ofthe lung parenchyma, the proliferationwas classified as a tumor.

Nearly all of the peripheral lung tumors we have observedwere of similar morphology, regardless of size. Tumorsinvolving entire lobes and tumors confined to a small tissuevolume exhibited similar degrees of atypia and mixtures ofadenomatous and epidermoid elements. For this reason, wewere unwilling to subdivide these tumors into 2 groups,adenoma and carcinoma. Rather, we have preferred tocombine these tumors into 1 category and then to define thecharacteristics of that category. Despite obvious objections,the term “combined epidermoid and adenocarcinoma― ismost descriptive of these tumors. Although the validity of amalignant designation in some animals may be questioned,evidence of local invasion (stromal connective tissue of thehilum, and venous, arterial, and pleural invasion) wascharacteristic of these tumors as a group and was demonstrated in many of the animals. Distant metastases wereobserved in I case. Furthermore, in preliminary experiments, Margaret Terzaghi in this laboratory has succeededin transplanting and growing tumors either s.c. or in thecheek pouch from a high proportion ( > 75%) of pulmonarynodules excised from polonium-treated hamsters. Reinjection of the tumor cells i.p. led to extensive peritoneal seedingand reinjection i.v. led to metastatic spread to the lung. Thehistological appearance of the transplanted tumors wasadenocarcinoma with varying degrees of differentiation.

The combined epidermoid and adenocarcinomas weregenerally peripheral in location, and both histologicalelements were intermixed (although to widely differingdegrees among animals) in all parts of the tumor. None ofour animals had so-called “collisiontumors.― The tumorsshown by Saffiotti et al. (19) in their Figs. 20 and 21, and 25to 28 are examples of more peripheral tumors, which wewould probably have classified as combined tumors (compare with our Figs. 9 to 11). Our purpose in thesecomparisons is not to be contentious, but rather to illustratethe similarities between their findings and ours, despitedifferences in terminology, and to point out the need for astandard classification for hamster lung pathology.

Although moderate chronic pulmonary inflammatorychanges were present in hamsters from all groups, tumorinduction by BP or the lower doses of 210Po (Groups 4 and5) was not associated with the production of lung damagesuch as extensive pneumonitis, necrosis, or interstitialfibrosis. This finding, along with the overall tumor mcidence, is consistent with the findings ofothers (19) followingBP-hematite administration. It differs, however, from previous experience with experimental lung cancer followingradiation in general and exposure to a-radiation in particular. This experience has generally shown that, in order toinduce a high incidence of lung tumors in experimentalanimals, lung tissue must be exposed to a very highradiation dose—one associated with the production ofconsiderable acute tissue dam age.

For a-radiation, Lisco (9) found a high incidence of lungtumors in rats exposed by inhalation to 239Pu in amountsthat yielded a very high radiation dose. However, this

NOVEMBER 1974 3031

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

J. B. Little and W. F. O'Toole

exposure was associated with the production of severeinflammatory changes, necrosis, and fibrosis in the lungs.Bair et al. ( I) also found a high incidence of lung cancer indogs that received 2,500 to 23,000 rads to the lungs from239Pu. With lower radiation doses. Yuile et a!. (25) foundlung cancers in I3% of rats that had received 538 rads to thewhole lungs from inhaled 210Po, and Temple et al. (23)found malignant lung tumors in only 2 or 8% of 25 mice thathad received a dose of 2,300 rads from intratracheallyinstilled 239Pu. Exposure to @-or rny-emitting radionuclides,on the other hand, has resulted in a significant incidence oflung cancer only following doses of several thousand up to10@rads or more (3, 22).

The reason for the unusual sensitivity to radiationinduced lung cancer (53% tumor incidence following 300rads) which we observe is not clear. It could be related eitherto the species or strain of animal, or to our particularmethod of administration which may allow the ratioactivityto reach and irradiate the critical cell populations in thelung. To our knowledge, no other data have been publishedon the sensitivity of Syrian hamsters to a-radiation. Wehave found only small differences in the lung cancersusceptibility of 4 inbred strains of hamsters to intratracheally instilled 210Po (10). In the present study, hematitealone did not induce lung tumors, nor did it appear, inspecially designed experiments, to exert a significant cocarcinogenic effect with 210Po (12). Furthermore, in preliminary experiments, 210Po administered alone in 0.9% NaClsolution proved at least as carcinogenic as that administeredon hematite particles (12). 210Po administered in 0.9% NaCIsolution leads to a much more uniform distribution ofradiation dose throughout the lung. The results suggest thatthe hamster may be particularly susceptible to the inductionof lung cancer by a-radiation at doses that do not produceconcomitant lung damage, and may, therefore, be a goodmodel for the study of the interactions between radiationand chemical carcinogens.

ACKNOWLEDGMENTS

We thank Dr. Robert B. McGandy and Dr. l-Iermann Lisco for adviceduring the preparation of this manuscript, and Stephen Donovan andJaruna Banaitis for expert technical assistance.

REFERENCES

I. Bair, W. J. Inhalation of Radionuclides and Carcinogenesis. In: M. G.Hanna, Jr., P. Nettesheim, and J. R. Gilbert (eds.), InhalationCarcinogenesis, Atomic Energy Commission Symposium Series, Vol.18,pp.77-101,1970.

2. Boyd, J. T., Doll, R., Faulds, J. S., and Leiper J. Cancer ofthe Lung inIron Ore (l-Iaemitite) Miners. Brit. J. Ind. Med., 27: 97- lOS, 1970.

3. Cember, H. Radiogenic Lung Cancer. Progr. Exptl. Tumor Res., 4:25l@303,1964.

4. Della Porta, G., KoIb, L., and Shubik, P. Induction of Tracheo-bronchial Carcinomas in the Syrian Golden Hamster. Cancer Res., 18:592-597, 1958.

5. DeVilliers, A. J., and Windish, J. P. Lung Cancer in a FluorsparMining Community: I. Radiation, Dust and Mortality Experience.Brit. J. Ind. Med., 2!: 94-109, 1964.

6. Dontenwill, W. Experimental Investigations on the Effect of CigaretteSmoke Inhalation on Small Laboratory Animals. In: M. G. Hanna,Jr., P. Nettesheim, and J. R. Gilbert (eds.), Inhalation Carcinogenesis,

Atomic Energy Commission Symposium Series, Vol. 18, pp. 389-4 12,1970.

7. Dunn, T., Kuschner, M., Mohr, U., Nettesheim, P., Stanton, M., andTurusov, V. Panel Discussion: Recommendations for Classification ofLung Tumors in Animals. In: P. Nettesheim, M. G. Hanna, Jr., and J.w_ Deatherage(eds.),Morphologyof ExperimentalRespiratoryCarcinogenesis. Atomic Energy Commission Symposium Series, Vol.21, pp. 451-472, 1970.

8. Kennedy, A. R., and Little, J. B. The Transport and Localization ofBenzo(a)pyrene-Hematite and Hematite-210Po in the Hamster Lung.CancerRes.,34:1344-1352,1974.

9. Lisco, H. Autoradiographic and Histopathologic Studies in RadiationCarcinogenesis of the Lung. Lab. Invest., 8: 162—170,1959.

10. Little, J. B., Grossman, B. N., McGandy, R. B., and O'Toole, W. F.Influence of Genetic Strain on the Induction of Lung Cancer inHamsters by Alpha Radiation. European J. Cancer, 9: 825-828, 1974.

11. Little, J. B., Grossman, B. N., and O'Toole, W. F. RespiratoryCarcinogenesis in Hamsters Induced by Polonium-2l0 Alpha Radiation and Benzo(a)pyrene. In: P. Nettesheim, M. G. Hanna, Jr., and J.w. Deatherage,Jr. (eds.),Morphologyof ExperimentalRespiratoryCarcinogenesis, Atomic Energy Commission Symposium Series, Vol.21, pp. 383-394, 1970.

12. Little, J. B., Grossman, B. N., and O'Toole, W. F. Factors Influencingthe Induction of Lung Cancer in Hamsters by Intratracheal Administration of “°Po.In: C. L. Sanders, R. H. Busch, J. E. Ballou, and D.D. Mahlum (eds.), Radionuclide Carcinogenesis, Atomic EnergyCommission Symposium Series, Vol. 29, pp. 119-137, 1973.

13. Little, J. B., and Radford, E. P., Jr. Polonium-2I0 in BronchialEpithelium of Cigarette Smokers. Science, 155: 606-607, 1967.

14. Little, J. B., Radford, E. P., Jr., McCombs, H. L., and Hunt, V. R.Distribution of Polonium-2l0 in Pulmonary Tissues of CigaretteSmokers. New EngI. J. Med., 273: 1343-1351, 1965.

I5. Lorenz, E. Radioactivity and Lung Cancer: A Critical Review of LungCancer in the Miners of Schneeberg and Joachimstal. J. Nail. CancerInst., 5: 1—15,1944.

16. Lundin, F. E., Jr., Wagoner, J. K., and Archer, V. E. Radon DaughterExposure and Respirato@y Cancer Quantitative and Temporal Aspects. NIOSH-NIEHS Joint Monograph No. I, June, 1971.

17. Martell, E. A. Radioactivity of Tobacco Trichomes and InsolubleCigarette Smoke Particles. Nature, 249: 215-217, 1974.

18. Radford, E. P., Jr., and Hunt, V. R. Polonium-210: A VolatileRadioelement in Cigarettes. Science, 143: 247-249, 1964.

19. Saffiotti, U., Cefis, F., and KoIb, L. H. A Method for the Experimental Induction of Bronchogenic Carcinoma. Cancer Res., 28: 104-124,1968.

20. Saffiotti, U., Montesano, R., Sellakumar, A. R., Cefis, F., andKaufman, D. G. Respiratory Tract Carcinogenesis in HamstersInduced by Different Numbers of Administrations of Benzo(a)pyreneand Ferric Oxide. Cancer Res., 32: 1073-1081, 1972.

21. Saffioui, U., Montesano, R., Sellakumar, A. R., and Kaufman, D. G.Respiratory Tract Carcinogenesis Induced in Hamsters by DifferentDose Levels of Benzo(a)pyrene and Ferric Oxide. J. NatI. CancerInst.,49:1199-1204,1972.

22. Sanders, C. L., Thompson, R. C., and Bair, W. J. Lung Cancer: DoseResponse Studies with Radionuclides. In: M. G. Hanna, Jr., P.Nettesheim, and J. R. Gilbert (eds.), Inhalation Carcinogenesis,Atomic Energy Commission Symposium Series, Vol. 18, pp. 285-303,1970.

23. Temple, L. A., Marks, S., and Bair, W. J. Tumors in Mice afterPulmonary Deposition of Radioactive Particles. Intern. J. RadiationBiol., 2: 143-156, 1960.

24. Wagoner, J. K., Archer, V. E., Lundin, F. E., Holaday, D. A., andLloyd, J. W. Radiation as the Cause of Lung Cancer among UraniumMiners.New Engl.J.Med.,273:181-188,1965.

25. Yuile, C. L., Berke, H. L., and Hull, T. Lung Cancer FollowingPolonium-2l0 Inhalation in Rats. Radiation Res. 31: 760-774, 1967.

3032 CANCER RESEARCH VOL. 34

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

Induction of Lung Cancer by BP and a-Radiation

@@ V

,@r'@'y- J

..

.•4v@

-@

@ @‘

.-,-@-I—.

. ,çI f@

‘ . ‘,

r.@@.a_ @h@'

-4'

I .

/ ,‘S.

.1 @fr6.@.@

@T @t

-‘

@:-@‘@-‘--@@

‘.1.@ —‘V—@

@ @â€.̃@ .@

-.@

.@ ‘@%I•@ @‘

@ -,,,7' ..@

—

...S

Sr.

I1@

il@

— ‘@,

@@ ‘

a

“1'

A

k I

..

t@.-,.-—-@ ,,

ft@. . .. .

@ /:.-:@t..

\@-. . •e

-.@ -

@ , @†@̃v:

, -. . .,‘ ..%.

, . - 0• -@

. ‘JeA ‘@ .@ •‘.@I@

@-- -P1;-.

@ @;@@f* .

@ ..@

@@ •@

@ ,

-.,@-@,@.—--@--@

‘@:1.@‘‘. ,@@

# 4.',.-@ 1@ .v@@ p

, I@ . - ‘@

. - @‘@@C―@@ ‘

, ‘@..@@ .@@ \

p@0@ . .,

@@ ,.

@@ .,@@ @.@ o'@@

@ ‘V. @ô‘!@A'@‘@- ‘

@ @&1@@ \@@ •@,

@‘

, ,‘s‘@‘:@@@ ‘::-;@@@@‘@ -. .@(; •.,,v:7@5,

@ , ‘‘:@@@@@

- ‘@@ - , ..—..@; ..—@.-.-@

c_p1@.,',@

@ ‘@@ I

&@I-•'S• .

NOVEMBER 1974 3033

?) ‘@..@v(@)

1@ f ‘@•@

@ ,# @‘

t@y

. .-. @ii@%@ a;@_@

@ :@@

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

J. B. Little and W. F. O'Toole

I ••,,. •@.@#:v.. p -

Id,@@ -,..-, OS, • . (I. a, ,, a

,@ ,@ ,,,@- 0@@ S

.5. ‘1 f@ ‘r-r.@-.' ‘.-

@. .1%•@ @,@ -,@ S.

@@ ;@

‘I@

-‘p@.@ 2.4@.

.1@'@

,t •@

@ p

I@ @:‘@:@,@e.@ @: @--.@ ‘;_1..___.;._@@% •@ @-.

%@@@

.@@ .--

, -. . :t@ _ . --t ‘; . ,.-- ,.@ - @.-,- I-.@

t -@@@@@@ -@.,@

a-a?@ @, @: •@...:;@ .--. ‘@-_.,. . ,._ :‘ :: ...@ .:

@ . @.,@ •@@@@

.. •:@@ S@ ‘@

. .@...--, -@ • -.- .--

. -@ .•_ ‘ --._@ @_,@ . .

:@@ I.‘ . .5.- . ‘@“V@

$,@@

-@@ :v@@;L.@e @S

@:- 11@@iL@ t'P@

-‘

,- ‘@b -‘.-- ‘_.@ .

.@ -- “p

3034

‘@c@@#a . @! •i@

., :..

•‘t•

.,-

.-.@-.---,‘,-.•-@

. @-..;J i..@. •.@@‘?@ @q'@

C' S@@

St

- @h @.4, •@,/ 1.' ,@,c,,5@

4 5S-@@

CANCER RESEARCH VOL.34

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

Induction of Lung Cancer by BP and a-Radiation

@s- ;J.h:@@@@ @.S@@

@I @r . •, :‘ @‘@--@ @.- :‘v@A@.'4I@- 4 t. .b

a r@.:@@ ;‘@ ,(.@ .4 4@ I@LII@

@1@@@ :. ‘. a ‘ @‘@ , S@.@ @4$@1

,(( ‘•,@ ‘.@ s@4@

‘5' ‘@ .?.* E@&@ -.

. 1I\@@@ ;@@

t@ •@@@ .:

@@@ @@r•,'It@@ @(@@ :‘@@‘. @-:@@@

.-t

NOVEMBER 1974 3035

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

J. B. Little and W. F. O'Toole

Si

.-@ .,-. p.

@ 1. ‘:@,@ ;@

@@ .-. -

& - ,@

h-1@@

‘,I.@

r.@@i--.: ‘@ ,@-

;.; @, .

CANCER RESEARCH VOL.343036

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

Induction of Lung Cancer by BP and a-Radiation

-@-@@ .5 y f@;1@,i;c@f

.@u.p, I..%4i@

@ I,, •@4•

@ I;.,-@@ .-‘

. .5 . •@,-:@ .@@ . ,@)• @.,.4 ‘@

4'.@ -

NOVEMBER 19743037

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

J. B. Littleand W. F. O'Toole

. a. C,@& I

S , ‘e@•@:@

.A@ a‘4'

:4*t ,@

. .a . .- ,@ ,*. •.@‘@:‘@ @i

- ‘. @, @1

‘ @-

.@ ,..p.., . ;@L

.5@@ ‘a -@-d ‘s,',@@

.@ :. @..

.. . .., .@ :,@. :@@ ‘.@. * ‘.

@14@ •.,@@@@ ,@-@ -‘.@fP@@@@ IP@

S.@@ ‘@ -. -@ -‘-S ••‘@@‘@‘@@ — S

@ @‘5-.@ ‘@:•.@ 5, F?-.@t'@ --.

:@@‘;;r―.@-.4@;;:@:@,.@ :‘@14•C.)@ . ,. , . -Cr.., •L@s.

. .- ‘,. . “ .—@@ %‘@@ .-.-b, C'5

:•..@,::.a a@@@@, ,@ I, ‘4;- -@@ .@@ - “@@

•@@“.:;@ .‘-@ @. . ‘ .- .. ..@

I

-.@@ .@

@10@@@ _(

@-@:_@@@@ :@@@ -

55 -: - -@@ ‘@ - .@ :4.'.

@@@ @-‘:‘@@@.::-“‘j-.@:c―@@‘.

t@:‘@@@@@@@ ‘@@

@@ •@ @-. I ‘@@@ ? - ‘4

‘@ “1e@i::\ ‘ . 1.1@

a •@@ C@ . . - -@ . C

3038 CANCER RESEARCH VOL.34

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

..._@.;.@ @‘r‘ --:- • . -;9. . @!@@@

‘-@‘@@-‘;.@@

.‘ . 1@@ ::r.-―@ @.

,-@ 4-. ‘.%@•‘. .5 @‘ .. - ‘ -

@ ...‘iS.@

-c c@@@@ ,—

-@@ b@

.. - ,@ @-.‘.,

@a..i:@1@@..‘@ ‘.-“@@ ::

@@ C

i'-- .- @.,4;j@'qp@@@ ;a@

•.@ & :@@ - :@@ •-a@

‘. . . . .@ .., .@4@@

@.@ ‘1%@@ ‘:) QI@ ‘5―@@:f,5@

,•@ @‘@;‘@. , a.—--.@ @:

. ;::;,c;0@,@.@.\@ 4•-,I'I―@ S

@ :E1@:r@@@

C @.@ @. @‘ •@: @‘@ - @-

a@@@ .@@ p__p. @,

, I @@@L%4a@@@

a ‘a.-@ ,•,@ 0-:: •@ @‘C@@ @e .

4 C S t •@.,@@ ;,. •?•@

@ ‘@@ @rt .@ .@ ‘ 1'

@. @.m@ - .

Figs. I to 12. All sections were stained with H & E except for those shown in Fig. 9. Sections in Figs. I to 8 and Fig. 12 were all from BP-treated hamsters, while those in Figs. 9 to I I were from “°Po-treatedanimals. The time of death is given in weeks after the 1st instillation.

Fig. I. Carcinoma in situ of trachea. Hyperplastic epithelium with central area of epidermoid carcinoma in situ with nearly complete lack of orderlystratification and marked nuclear variation (Group 6, 20 weeks). x 100.

Fig. 2. Tracheal epithelial hyperplasia (Group 6, 15 weeks). x 250.Fig. 3. Trachea. Broad sheets ofepidermoid carcinoma can be traced from Iuminal surface on right to adventitial tissues deep to cartilage (Group 6, 53

weeks).x 125.Fig. 4. a, poorly differentiated epidermoid carcinoma in lung; b, exfoliation oftumor cells into lumen ofintrapulmonary bronchus (Group 6, 36 weeks).

x 100.Fig. 5. Spindle-cell tumor of trachea. The spindle cell and stratified squamous components are closely intermingled (Group 6, 15 weeks). x 125.Fig. 6. Spindle cell tumor of trachea (Group 6, 27 weeks); a, cross-section of trachea with invasion of noncartilaginous portion of wall by spindle-cell

tumor with papillary intraluminal component. x 25; b, detail showing relationship of tumor to stratified squamous epithelium. x 100; c, metastasisin peripheral sinus of cervical lymph node. x 100.

Fig. 7. Marked terminal bronchiolar epithelial hyperplasia similar to “adenomatoid―lesion described by Saffiotti et al. (19) (Group 6, 83 weeks).x 125.

Fig. 8. Combined epidermoid and adenocarcinoma in BP-treated hamster showing expansile growth pattern. Close observation reveals infiltrating nature of tumor. Note absence of hematite aggregates in areas where lung parenchyma is replaced by tumor (Group 6, 28 weeks). x 25.

Fig. 9. Combined epidermoid and adenocarcinoma (Group 4, 45 weeks); a, lung tumor composed of alveoli with tall cuboidal and columnar epithehum and nests of solid tumor (periodic acid-Schiff, x 100); b, tumor acini closely associated with fields ofepidermoid-type carcinoma. Both this and thepreceding field demonstrate relatively benign cytology of this tumor (periodic acid-Schiff, x 100); c, medium-sized muscular artery in lung invaded bytumor that fills the entire lumen (Verhoeff-Van Gieson, x 100);d, tumor at pleura with overlying pleural fibrosis at right. Note breaks in pleural elastictissue layer (stained black) and invasion by tumor. (Verhoeff-Van Gieson. x 100.)

Fig. 10. Combined epidermoid and adenocarcinoma (Group 4, 21 weeks); a, there is acinar formation and patchy mucus production in addition to nestsof tumor cells with sharp cell borders and stratification, suggestive of epidermoid carcinoma. x 125; b, in this region, pattern is predominantly epidermoid with keratin pearls. Comparison between Fig. 10 a and b, illustrates the marked variation in different areas of a mixed tumor. x 125.

Fig. I I . Combined tumor showing interface between epidermoid pattern on left and adenomatous pattern on right (Group 5, 78 weeks). x I25.Fig. 12, a, small-cell anaplastic carcinoma (Group 6, 35 weeks). x 100; b, small-cell anaplastic carcinoma (Group 7, 64 weeks) x 250.

Induction ofLung Cancer by BP and a-Radiation

NOVEMBER 1974 3039

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from

1974;34:3026-3039. Cancer Res   John B. Little and William F. O'Toole 

-RadiationαPo 210)pyrene and aRespiratory Tract Tumors in Hamsters Induced by Benzo(

  Updated version

  http://cancerres.aacrjournals.org/content/34/11/3026

Access the most recent version of this article at:

   

   

   

  E-mail alerts related to this article or journal.Sign up to receive free email-alerts

  Subscriptions

Reprints and

  .pubs@aacr.orgDepartment at

To order reprints of this article or to subscribe to the journal, contact the AACR Publications

  Permissions

  Rightslink site. Click on "Request Permissions" which will take you to the Copyright Clearance Center's (CCC)

.http://cancerres.aacrjournals.org/content/34/11/3026To request permission to re-use all or part of this article, use this link

Research. on January 10, 2020. © 1974 American Association for Cancercancerres.aacrjournals.org Downloaded from