smoking-related cancers and potential years of life lost attributable to cigarette smoking, ireland,...

SMOKING-RELATED CANCERS AND POTENTIAL YEARS OF LIFE LOST ATTRIBUTABLE TO CIGARETTE SMOKING, IRELAND, 1968 to 1978

D. Haslett

Department of Community Health, Trinity College, Dublin.

Summary ATTRIBUTABLE risks within maximum

and minimum limits were calculated for six smoking-related cancers in Ire, land-- lung, larynx, oesophagus, bladder, kidney, and pancreas. From these calculations were derived potential years of life. lost to Irish men and women aged between 30 and 64 years from each cancer site which could be directly attributed to cigarette, smoking. The relationship between the. calculat:ed attributable risks and the, potential reduction of disease are, discussed from a public health point of view.

Introduction A vast number of epidemiological

studies, both prospective and retrospective, and 'a number of pathological and experimental studies have, produced evidence which implicates cigarette smoking as a risk factor for cancers of several sites, including lung, larynx, oesophagus, bladder, kidney, pancreas and oral cavity (Report of the Surgeon General 1982). Each year in ~reland a number of men and women die prema- turely from these diseases. Many of these deaths can be attributed to cigarette smoking and are therefore poten- tially preventable,. Many of these deaths occur in men and women in the, prime of their productive, life and are, therefore a considerable social /economic loss to the community as a whole as well as a personal loss to their families. It is the purpose, of this paper to examine premature mortality from smoking related cancers and to estimate the proportion of potential years of life which are prema-

turely lost each year from these cancers and which can be directly attributed to cigarette smoking.

Methods (a) Calculation of Potential Years of

Life Lost (P.Y.L.L.) When discussing the impact of prema-

ture mortality it is important to give weight both to the age at death and to the actual age structure of the population being considered as well as the number of deaths. As. an indicator of premature mortality this study uses a modified form of Romeder and McWhinnie's (1977) equation rather than numbers of deaths per s e, (see: Appendix A). A premature death was defined as a death between 30 and 64 years and the reference population used in the equation was. the 1971 census. This equation was applied to the following mortality data.

(b) Mortality Data Mortality data for the following smok-

ing-related cancers by sex and age. group for the, years 1968 to 1978 were obtained from the annual Reports of Vital Statistics (cso). ICD No. (8th Rev.) Malignant Neoplasm

162 Lung 161 Larynx 150 Oesophagus 188 Bladder 189 Kidney 157 Pancreas

Because of the very small numbers of deaths from malignant neoplasms of the oral cavities these cancers were ex-

302

Volume 153 Number 9 Smoking rela,ted car~cers in Ireland 303

cluded from consideration in this study. Deaths which occurred under the. age. of 30 (of which there were very few) were not included.

(c) The Estimation of Attributable Risks In order to estimate the proportion of

PYLL for each cancer which can be. attributed to cigarette, smoking, appropriate attributable risks were calculated. The term "attributable. risk" is defined in different: but closely associated ways by Walter (1978), Cole and MacMahon (1971) and Miettinen (1974). The defin- ition used in this study is a slight modi- fication of that expressed by Walter as follows :

p(rr-I) AR% -- x 100

p(rr~l) +1 where AR% = attributable risk per cent

p = proportion of population exposed to the risk (ie cigarette, smoking)

rr = relative, risk

Ideally good prospectively collected data will allow the calculation of both (p) and (rr') provided that the sampled individ- uals were not stratified by exposure, to the. risk in question. Where these data are not available then it is necessary, and' possible., to estimate (p) and (rr) from other sources.

(c.i) Estimation of (p) for an Irish population

Since. 1972 the Health Education Bur- eau has routinely carried out annual surveys of smoking prevalence in the population. Ideally one would like to have available smoking prevalence data for the, appropriate age groups in the 1950's but in the absence of this the best (if somewhat conservative) estimate, of smoking prevalence at that time. is probably the current prevalence of 45 to 64 year olds who were almost certainly smoking 20 to 30 years ago.

Walter (1978)and Lilienfe, ld and Lilien- feld (1980) have. demonstrated that even

if the (smoking) proportion is not known with great accuracy a crude calculation can be used with little effect on the attributable, risk provided the population expqsure rate is reasonably high. Only if the exposure, rate proportion is very low (eg .05, .10) can small changes in exposure, have significant effects on the attributable, risk. The male and female proportions used in the calculations of attributable risk percentages in this study were .49 and .37 respectively (HEB Sur- vey 1972).

(c.ii) Estimation of (rr) for each disease

With regard to estimating ( r r )s for a population which has neither prospective nor retrospective data available Walter (1978) points out that if a relative. risk is regarded as "a biological constant which would apply in a variety of circumstances.-- (and) D if this constant relative, risk can be estimated it may then be used in combination with a previously determined percentage exposed to risk appropriate, for the population of interest". In other words if one thinks of the variation between studies in the estimates of relative risk (or odds ratio) for cigarette smoking as being due. to sampling error and that the same "true" relative, risk applies to each population studied, then it is theoretically possible to apply the relative risks for one population to another in order to derive attributable risks. On the basis of this theoretical proposition it is assumed here that-at t r ibutable risks associated with cigarette smoking in relation to specified cancers can be, calculated for Ireland using estimated relative risks for other studies and population exposure proportions as derived from HEB smoking surveys. Appendix B, Table B.I shows the set of relative risks which have been used in this study. These are the maximum and' minimum relative values for each of the six cancers which have been derived from seven major prospective studies carried out

304 Haslett I.J.M.S. September, 1984

APPENDIX B TABLE B.1

Smoking-related; cancers : maximum and minimum relative risks for cigarette smoking derived from seven major prospective studies, by sex and

c~ncer site.

Males Females

Cancer site Max. Min. Max. Min.

Lung 14.2( 4 ) 7.0'(7J 5.0~( 1 ) 3.58( 2 )

Larynx 13.0( 1 ) 6.52( ~ ) 3.25,(~) *

Oesophagus 6.43.(3) 1.82(~) 4.89(~) *

Bladder 2.89'(6~ 1.4(~) 2.8(2~ 1.6,(7)

Kidney 2.66(J) 1.42'(~) 1.5"*

Pancreas 3.1 (7) 1.5 5) 2 .5 (7 ) 1.4(3)

(1) British Physicians Studies (Doll and Peto, 1976, '~'o,II et al, 1980).

(2) Amer);an Cancer Society 25-State Study (H"am-lond ~, 1966)

(3) U.S. Veterans (Dorn, 1959; Kahn, 1966; Rogot and Murray, 1980)

(4) Canadian Veterans Study (Best, 1966). (5) American Cancer Society 9-State Study

(Hammond and Horn, 1956) (6) Californian Males in Various Occupations

Study (Weir and Dunn, 1970') (7) Probability Sample Study of Swedish Popu-

lation (Cederlof et al, 1975)

* Only one prospective value available. ** An odds ratio derived ~ retrospectively from

Wynder et a! (1974) due to the lack of appropriate prospectively derived relative risks.

since the 1950s in Britain, Sweden, Can- ada and' the USA. An eighth major study, Hirayama's (1972) prospective study of Japanese men and women was not included because of the tendency for its relative, risk estimates to be either very much larger or very much smaller than the European / American studies. This study assumes that the "true" (rr) lies somewhere between these maximum and minimum values.

Results In the tables given below results are

reported for every second year from 1968 to 1978.

(a) Premature Mortafity from Smoking-Related Cancers

Table I(a) and I(b) below show premature deaths (30 to 64 years) from all diseases as a proportion of all deaths (30+ years) and premature deaths for each cancer site as a proportion of all deaths for each cancer for males and females.

Fro m these tables it can be seen that for males the proportion of premature deaths for each cancer site is greater than the proportion of premature deaths for all diseases with the exception of bladder. For females on only one occas- ion did the proportion of premature deaths for a cancer fall below the pro-

TABLE I(a)

Males : Premature (30-64 years) deaths as a p.roportior~ of all d,eaths (30-t- years) for &ll diseases, and ~ premature deaths for each cancer site, as a proportion, of all deaths for that site by year.

All Cancer Site Diseases Lung Larynx Oesophagus Bladlder Kid'ney Pancreas

1968 .27 .48 .18 .34 .22 .28 .33

1970 .28 .51 .30 .33 .26 .50 .34

1972 .27 .45 .27 .42 .16 .49 .33

1974 .27 .38 .33 .27 .17 .43 .36

1976 .26 .40 .28 .35 .33 .42 .37

1978 .26 .37 .48 .35 .24 .60 .28

Calculations derived from data published = in Reports or[ Vita,l Statistics, CSO, 1968-1978.

Volume 153 Smoking related cancers in ~re~and 305 N u m b e r 9

TABLE I(b)

Females: Premature (30-64 years) deaths as a proportion of all deaths (30-t-years) for all diseases, and premature deaths for each cancer site, as a proportion of all deaths for that site,

by year.

All Cancer Site Diseases Lung Larynx Oesophagus Bladder Kidney Pancreas

1968 .20 .50 .33 .37 .29 .54 .25

1970 .21 .46 .71 .26 .32 .38 .29

1972 .19 .44 .46 .40 .21 .48 .29

1974 .19 .39 .56 .32 .09 .36 .24

1976 .18 .39 .25 .30 .21 .33 .26

1978 .18 .40 .50 .32 .27 .44 .30

Calculations derived from data published in Reports on Vital Statistics, CSO, 1968-1978.

por t ion of p remature deaths for al l diseases. Many of these premature deaths are undoubted ly caused by c igaret te smoking and are undoubted ly prevent- ible.

(b) PYLL from Smoking-Related Cancers Premature deaths for each si te were

conver ted into potent ia l years of l i fe lost (PYLL) as a l ready descr ibed. Table II be low shows ( i ) the rate of PYLL (standard ized to 1971) summated across the s ix cancers, ( i i ) the rate of PYLL for al l

d iseases and ( i i i ) the former as a percentage of the latter.

This percentage increased over the l 1-year per iod under study for both males and f e m a l e s - - f r o m 8.4% to 10.4% for males and f rom 5.6% to 6.9% for females.

(C) PYLL from Smoking-Related Cancers which can be Attr ibuted to Cigarette Smoking

It has been demonst ra ted so far that smoking-re la ted cancers are associated

TABLE II

Rate of potential years of life lost (per 100,000 pop. standardised to 1971) for (i) all diseases, (ii) smoking related cancers aggregated' and (ii i), (ii) as ar percentage of (i), by sex and' year.

i

Males Females

( i ) ( i i) ( i i i) ( i ) ( i i ) (iii) all S-R (ii) as all S-R (ii) as

diseases cancers % (i) d'iseases cance,~s % (i)

1968 76.20 643 8.4 5323 299 5.6

1970 7824 761 9.7 5197 297 5.7

1972 7746 651 8.4 5002 350 7.0

1974 7545 685 9.1 4629 320 6.9

1976 6691 719 10.8 4227 326 7.7

1978 6902 735 10.7 4111 283 6.9

Calculations derived from d'ata published in, Reports on Vital Statistics, CSO, 1968-1978.


with above average premature mortality and that PYLL for smoking related cancers is increasing as a percentage of PYLL for all diseases for both males and females. The final stage, is to determine what proportion of these. PYLL can be. attributed to cigarette, smoking. Table, III below shows maximum and minimum attributable risk percentages to be used for Irish mortality data which were derived according to Walte.r's (1978) equation (see Methods section).

TABLE III

Maximum and! minimum attributable risk percentages for cigarette smokin~g, by sex and cancer

site.

Male Female Maximu,m Minimum Maximum Minimum

Lung 86 75 60 49

Larynrx 85 73 45

Oesophagus 73 29 59

Bladder 48 16 40, 18

Kidney 45 17 16

Pancreas 51 20 36 13 i i

When these maximum and minimum estimates are applied to the PYLL as calculated for each cancer site., the resulting PYLL are, taken to be, the PYLL due to cigarette smoking. Appendix B, Tables B.II(a) to B.II(f) show the maximum and minimum limits for male,s and females by cancer site.

When the PYLL attributable, to smoking for each cancer site are. summate.d and compared to the total PYLL for each site, (Table. IV) then we can see, that for males between 61% and 77% of PYLL due to smoking-related cance;s are directly attributable, to cigarette, smoking. For females the corresponding limits are, 41% and 51%.

Discussion The results of this study estimate.

(within maximum and minimum limits)

TABLE B.2

Maximum and minimum rate, of potential years of life lost (per 100,000 pop. standard,ized' to 1971 ) attributable to cigarette smoking for each cancer

s, ite, by sex and year. = , l

Male Female

B.2 (a) Lung Max. Min. 1968 403 352 1970 479 418 1972 387 338 1974 394 343 1976 406 354 19,78 416 368

B.2(b) Larynx 1968 6 5 1970 12 11 1972 9 8 1974 14 12 1976 18 15 1978 28 24

B.2 (c) Oesophagus 1968 28 11 1970 37 15 1972 41 16 19,74 32 13 1976 37 15 19'78 52 21

B.2(d) Bladder 1968 11 4 1970 15 5 1972 10 3 1974 7 2 1976 18 6 19.78 18 6

B.2(e) Kidney 1968 8 3 1970 10 4 1972 20 7 1974 17 6 1976 17 6 1978 22 8

B.2 (f) Pancreas 1968 45 17 1970 43 17 1972 3.5 14 1974 58 23 1976 51 20 1978 31 12

Max. Min,. 87 71 90 73 98 80

112 91 112 91 96 78

35 24 39 23 28 24

5 2 5 2 5 2 3 1 4 2 3 1

15 5 21 8 27 10 21 8 17 6 17 6

the potential years of life lost to Irish men and women between 30 and 64 years from cancer which is directly attributable to cigarette smoking. From

Volume 153 Number 9 Smoking related cancers in Ireland 30,7

TABLE IV

Rate of potential years of life lost (per 100,000 pop. standardized to 1971 ) attributable to (1) all smoking related (s-r) cancers, (2) all smoking-related cancers as a direct consequnece of cigarette

smokir~g (maximum and' minimum limits) by sex and year.

Males Females

(1) (2) (1) (2) All s-r Attributable to All s-r Attributable to

ca r~cers smoking cancers smoking

max. min. max. min.

1968 643 501 403 299 152 123

1970 761 596 485 297 152 119

1972 651 502 403 350 178 140

1974 685. 522 412 320 164 131

1976 719 547 431 326 171 135

1978 735 567 466 283 145 114

where d i = numbers of deaths between ages a i = remaining years to age 64 where

= 65--(i +2.5) Pi = number of persons aged between Pit = number of persons aged between N r = number of persons aged between

APPENDIX A

The age-adjusted rate of F;YLL was calculated as follows :

(,,/(P_,t AGE-ADJUSTED RATE OF PYLL = ~ a i x 100,000 \P, / \Nr /

i = 30, 35 . . . 60

i and i+4 death occurs between ages i and i+4

i and i-l-4 in actual population i and i+4 in the reference population 30 and 64 in, the reference population

the, pub l i c heal th po in t of v iew these est imates are of in terest prov ided the. es t imated a t t r i bu tab le r isk pe rcen tages bear a high re la t ionsh ip to the actual reduc t ion in d isease (and the cDnse- quen t probable, sav ing of years of l i fe) wh ich wou ld be expected ' to occu r if e x p o s u r e to c igare t te smok ing were p reven ted or even reduced. Th is rela- t ionsh ip d e p e n d s on the ex ten t to wh ich the r isk fac to r here can be shown to be a causal agen t of the d isease (MacMahon and Pugh, 1970). As Wal te r (1978)po in ts out " i f the [ r isk ] f ac to r is a causal age,nt of the, d isease and the, r isk in quest ion

is d is t r ibuted in the popu la t ion independent ly of all o ther causal r isk factors, then the, reduct ion and the a t t r ibu tab le r isk are equal. On the o ther hand if r isk factors are con founded , then the. at t r ibutable, r isk wi l l be e i ther g rea te r Dr lesser depend ing on w h e t h e r the con found ing is pos i t ive or nega t i ve" . On the basis of a major rev iew of ep idemio log ica l , patho- log ica l and exper imen ta l ev idence, the Repor t of the Su rgeon Genera l (1982) conc ludes that smok ing is the ma jo r cause of lung and laryngeal cancer , a ma jo r cause of oesophagea l cance r and that in the cases of b ladder , k idney and


pancreatic c a n c e r s " c i g a r e t t e smoking is a contributory factor" by no means excludes the possibility of a causal role for smoking in cancers of this site r''.

With regard to bladder cancer the Report concludes that "cigarette smoking probably acts as an independent agent in the development of bladder cancer; however, there may also be additive or synergistic interactions between cigarette smoking and substances present in the work-place". With regard to kidney carcinoma Wynder et al (1974) in a review of the epidemiology of adeno- carcinoma of the kidney, suggested that apart from tobacco smoke, other aetio- logical factors in this disease included hormones, genetic susceptibilities, ioniz- ing radiation and elements such as lead. Finally, pancreatic cancer has been linked with diabetes mellitus, chronic pancreatitis and chemical exposures as well as tobacco smoke (Morgan and Wormsley, 1977). All of this evidence suggests that although there is un- doubtedly a relationship between the attributable risk and the reduction of disease for these three sites, these relationships are not as good as those for lung, laryngeal and cesophageal cancers where the evidence of causal- ity is much better.

Conclusion There can be no doubt that for lung

cancer (which is the largest of the, six sites in terms of PYLL, even at minimum estimates, for both males and females) the relationship between attributable, risk and the reduction of disease must be very high. In other words, if exposure to cigarette smoking had been prevented in the 1940s, '50s and '60s then current premature loss of life from cancer of this site would be very small. It is important to note that even with current falling population exposure to cigarette smoke r among both males and females (HEB Surveys 1972-1980) there will be mar- ked premature mortality from lung cancer

for some years to come. The most recent HEB survey estimates smoking proportions of .46 and .39 for males and females in the 25-34 age band. If these proportions persist without reduction for the next 20-30 years then these cohorts will be susceptible to premature death from lung cancer to almost the same extent as is currently affecting those. smokers who fell into this age band in t he 1950s.

Acknowledgements I would like to thank James McCormick and

John Haslett for their kind help and advice.

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Doll, R., Gray, R., Hafner, B. and Peto, R. 1980. Mortality in relatior~ to Smoking: 22 Years' Observations on Female British Do,ctors. British Medical Journal 280 (6219), 967-971.

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