Document qdNGLRdkDV1oJQgajg399Oj7n

. An Rfprymitd fromt the A. Sf. A. .irekivet *f fmdmtino1 ll***1^ 1958. Vil. 17. pp. 6J4-6SJ Copyright 1958, Itr Amfriton .\fthirof /isso*,*t,om from , c, , . ' IMUSWH HYC1EH f Epidemiological Study of uco Film Ave.. p,,tJi Luns Cancer in Asbestos Miners FOUNDATION IJ, Pa DANIIL Cm SAAUN, M.O.. T. OAVI0 nUAM, M.4_ PrmOmrg* Ever since the pronounced increase in the incidence of lung cancer a/nong ,-ruJes became apparent, there have been attempts to associate t with one or another of the vanous elements in the environment of man. The approach used by some workers has been to suspect one or several sub* stances and then set about in an intensive scarce tor lung cancer among persons who have rud any exposure to those materials. In this connection Smith n writes: "The tenae-.icv ot authors reporting the coinci dental occurrence of pnrrury Jung cancer with siiicojts or with any otner theoretical etioiogic conditions, has been to empnasue the percentage reiationship m extremeiv small series oi cases. with control cases which are not m any way comparaole." It would seem inevitable that asbestos should come under scrjtmy m this manner, because prolonged exposure to this material is known to cause a specific type of pneu* moconiosis, and because persons who show this form of pneumoconiosis often come to autopsy arid provide a ready source of material for study. It was in this way that reports of the simultaneous occurrence of lung cancer and asbestosis began to accu* muiate after the 'eport of a case by Lynch and Smith-** in 1935. Within the next JO years, about 15 additionaJ cases were re ported. and in 195-1 Merr'vether ?* reviewed ail deaths from asbestosis recorded in Eng land since March, 1924. Lung oncer ocairred in I6$e of these cases Glovne.41 Acseeitd for puJjliation /an. 70. I9S4. T%s matic possible ihrrxjqh 3 pnt Imm iIk ri'^l"^ Abeti* Minn- Afvcuuou. Weliol Otrrciur (Or flraun) ind Slanslroi Consultant fMr. Tnun), tnduirul Hygiene whose work is also frequently referred to as establishing a connection between asbestosis and oncer of the lung, reported m 1951 that cancer of the lung was present in 14.1 ^0 of asbestosis cases examined by him. In 2941, Nordmann and Sorge Tt claimed to have produced lung cancer in mice whicn they exposed to asbestos dust. Since 1951. additional cases of cancer of the lung coexisting with asbestosis have .been rercreb. and. according to Hue:;*: '* aooui ICC suc.i cases had been reported in* 10 J955. As a result, an association between the rwo diseases appears to have seen ac cented by many authors, and several writers were using tne term "asbestosis cancer" of the lung 'Veroer,** in 1952. suteo cate gorically that m 7Co to 17?b of cases or asoestosis. after a latent period of about \l/i to 20 years, carcinoma becomes estaolished m the lung. On the other hand, not ail authors ac cepted this alleged association without reservation. Saupe** m 1939 reported that he had discovered no cases of lung cancer among 620 cases of asbestosis whjcn he had examined: and in 1942. Hoileb and Angnst '* expressed the opinion that the numoer of cases of asbestosis with lung cancer was (no smai! for statistiai evalua tion. In L947, WegeJius M reported 126 radiolugictlly diagnosed cases of asbestosis among workers in Finland, and found no cases of lung cancer m this gTOup. Ooldblatt and Goldblatt in their section of Merewcther's latest book,*4 sate: "But at mo <f.ige m .nil these impressive researches wn.s any clue obtained which might hi*vi* offered any supj>ort to the possibdiry that 'rK-:cJ c'< ild k: at : u .. 614 `//V<r/ t. JJ.'SG CANCf.R IS ASUtiSTOS MINERS is no reliable cnknon by which one cn* .uil>ci|t.itc orcinugcnicH) and. as i$ well knnn, relatively mmuic changes in the structure of a chemical carcinogen are sum- cirnt 10 dimmish or eliminate ciircmugemc action. If asbestos is indeed lo be regarded as a arcinngeu. the nd is felt to denonstratc some property which van be regarded as something more ihan inertness.** These authors advance the theory that, until some more experimental evidence of direct carcinogenesis by asbestos or a deeunijostiiun product of it can be obtained, asbestos might be considered as a "co-careinngen'* which only induces a further de velopment of a preneoolastK condition brougru about by something independent of the Asbe'ios. >nch as an endogenous factor. Thus the Ineruure. wmie tending to -sup port the thesis that asbeMosis *s m some way related to the development of lung cancer, is by no iuons unanimous. Alto gether, a is perbaos more confusing than eniigntening. A careful review show* that the majority of the reports are climal and not epidemiological. They tack many ele ments necessary for the appHauon of epidemiologiol techniques to their content, and most of the authors do oo( make claim to having done so. What has happened i* that succeeding authors have drawn conciu* sions and generalized beyond the scoj* of the works which they quote. Nowhere, for example, have we found references to u population of asbestos workers, although several authors who have quoted lhe ob served incidence of lung cancer m uuiojimcsof perjons who also had ajbesiojis implv that this incidence applies to asbestos work ers. generally. We have likewise been unable 10 find any study which actually calculated the incidence of lung cancer among a population of person* who had asbestosis, and not just thoe who ctme tn autopsy. With the exception nf * jwij-er nol,.n none of those rexirwcd am iLia on exjosure and Just lOncniiruiiiHis, and c\cn Doll's paper merely mentions "scheduled'* :ircu>. by which i meant, "those areas where processes are carried on which were 'cheduied under the Asbestos Industry Kegul.uioii- of 1931 as being dusty.** There is, furthermore, a complete lack of definition of lemis as used in the published literature. For example, the term "Asbestoses. as used, may refer to changes observable only by microscopic examination of the lung tissue, or it may mean a radiologiciily detectable condition. Most of the published reports obviously included women among their cases, but -omc of them do not give the number or jro\>nrtion of women involved m the study. There is also a lack of uniformity as to what fsqw* of exposure most studies have dealt wth. Of 99 wc? enumerated by Muckier'* in 1955. wniv 10 appear :o have originated in the United Stales, and ' in Canada. Some of the earlier reports ap parently included asbestos miners, but it can be assumed, since 52 of the 99 cases had originated in England, and stnee no a*be*tos mmmg operations are carried on in that country, that most of the reported cases have involved workers in the texoie or fabricating industries. Such factors as smoking habits, family history of cancer, length of time in die industry, and age of the individual case are also notably absent in the majority of these reports. With this understanding of the limita tions of the existing literature *uh respect to epidemiological generalisation, it may be nf value to consider in somewhat more de tail <ome representative earlier publications, i few of which were referred to bnedy above. One of the most detailed studies and one which deserves the most serious considera tion is that reported by Dollu in 1955. This study reviews causes of death among .i-bestos workers based on coroners* rec- i.i.U, H jl-*> l. .n** >' Uie ii>* Uy -tu.lying records of men who worked for at least 20 years m exposed situations. /V 6J5 'f-l o ( .4. M. .4. /4Ri nn i..\ in iXnrsTKt.H. H/..4I.TH Doll concluded that lung cancer was a specine industrial hazard of certain asbestos workers and that, after 20 years of expo sure. the ruk is 10 times a- great as for the general j>opuiation. This article is important tor se\eral rea sons. in addition to the detinue conclusions at which it arrtves. For example. t begins by stating that "in view of the infrequency of asbestosis. this large number of cases 161 cases of lung cancer) suggests--but does not prove--chat lung cancer is an occupational hazard or asbe>(os workers." Neither this article nor any previous one which we have examined presents any fig ures to prove that asbesto*i> is an infre quent occurrence. Estimates of the number ot (Persons potenuailv exposed to asbestos dust :n the United States alone wry from lO.COO to 25.000. and :ne inciaence of asbestosis of any degree might be Higher than Doil imagines. This stud'*, like so nijnv others, involve* autopsv records. The number of person^ inxoUed in the statistical analysis is onl\ 113. representing only 1.042.25 man-years of life. It is also true that in selecting men who had been employed for at least 2(1 rears, the study automatically excluded those who died from other causes after shorter employment. Another reason why ihi< publication is of importance is a statement which it con tains to the enect '.hat "the strongest evi dence that n ilujig cancer) may be a hazard fin asbestos workers) has been produced by Merrwether and by Gloyne." In 1951 Gio^me*1 presented a review of 1205 autopsies on persons who had worked in various dusty occupations. This number included 132 asbestos workers, of whom 121 showed '`pneumoconiosis'*--pre sumably asbestosis. Primary cancer of the lung occurred 17 times m this group, an incidence rate of 14.1% for lung cancer among asbestosis cases coming to autopsy. There were in h>s series 796 cases with sdi--* 9% of thee also showed pri mary cancer of the lung The incidence of lung ranee r in other foetus of pneuutocomcrsis was 6.7/r. and in 169 cases which proved not to have any type of pneumo coniosis it was 8 y.'c- Gloyne considered "the mortality of the asbestos workers" to be "disturbing." First of all. it is obxiou' that the paper does not deal with :He "mor tality of asbestos workers." and secondly, it must be borne m mtnd that all of Dr. Gloyne s cases were submitted to him for study because the findings were unusual for uncomplicated pneumoconiosis. U an reasonably be assumed that ascs. including (hose of asbestosis. in which the findingwere unt considered unusual were not ?ent to Dr. Gloyne for examination. As a mat ter of fact, m the same paragraph m which he expre^e- concern over the incidence rate :n asbestosis. Dr. Glovne himseu points out that the rate for lung cancer bases on necropsies at the London Chest Hospital was 21.3% while the figures of the Registrar-General showed only 2.4Ce He thus recognized that autopsies on n vertarn ^elected group of cases were not re:*resentam e of the general population It would *eem. then, that notwithstanding the \aiue of Dr. Gloyne's work, its importance as an index of the prevalence of lung can cer in asbestotics has been misinterpreted by some who have quoted him. AM that u really shnw* is (he fac: that in a group of 121 C.Kcv selected for special study pri marily twenuse they >ecmed Abnormal by preluninarx cxannu.iitou. I", nr 14 I r\, Had lung <.rincer Merewether'1 m 1947. in the rrjion of (he Chief ln>|>ector of Factorio. reviewed all ca>c> rciiricd between 1924 and 19**6 m which asbcMOsis wa the cause of death or a mexistiog condition. This work was laicr extended in include all such cases relortcd up io December, 1954. bv which time (here were 344 Heaths, including 205 male-* and 139 females. Among them were 55 ases (.16%) of ancer of the lung. 41 m male* and M in females. It is quite jmssible that a large number of a-tw--i/vi.-* .*i-~ a\a not die nf their a*besiosts, or in whose 6J6 17, Jwmr }<9S!t J0 U'XG C.4\Cr.R IX .1SUCSTO* MIXERS death certificate it was not mentioned, may have been missed. The import of this 165< is enhanced by ihi- simultaneous statement that the incidence of lung cancer in autop sies of the general jiopulation is nnlv \%. The danger of lutenipting to compare a rate found in 5-U cases with the rate for the general population without respect to age. occupation, and many other variables, such as smoking habits, is obvious. Lynch.TM who with Smith M had reported the first ase in 1935. reported 4 cases of carcinoma of the lung in a series of 49 autopsies on workers in an asbestos mamafactoring plant who were shown to have 'demonstrable deposits of asbestos in the lungs.*' This, of course, is not necessarily identical with the disease asbevosiv Lynch, him.-ei;. points our tha:. although this is an incidence of S.2f<r. "both figures are too small for very serious statistical types of calculation." Xevenhctess. later writers have used this papeT to strengthen the ase for an association of carcinoma of the lung with asoestosis It is also of interest that Klotz u found only the same number of cases of lung cancer m a senes nearly 10 rimes as large, i. e., 4 in 4/8 cases of asbestosts. Behrens, as cited by Merewether.TM esti mated that, of 309 cases of asbestosis in the literature. 44 showed associated cancer of the lung-giving an incidence of 14 2%r. This is an illustration of generalizing an incidence obtained in a group of cases which were undoubtedly reported only be* catLse some of them showed lung cancer, to possibly hundreds of asbesrotics whose ases were never reported. The same ap plies to the conclusion of Teleky,** who appears to have reviewed reports of J9 autopsies on persons with asbestosts among which 6 cases of lung cancer occurred. In formation from sources such as these does not justify generalizations with regard to morality rates. Perhaps no one has written so exten sively on the subiect as has Keeper.1519 In 1953 He reviewed the cases * reported prior to that date and enumerated a total of 99 Eleven of these were those dis cussed by Doll :s and may have been cases covered by other authors. Eight were dis covered by Kennaway and Kennaway 11 in an analysis of death certificates, and. unless Merewether's study was incomplete, these cases should have been included in his re port. Of the remaining 80. it is quite pos sible that the 31 contributed by Merewether ajid the 17 by Qoyne contain some duplica tion with each other or with those of other English authors. Principles of the Epidemiological Method Dorn 30 has pointed out that much of what is now thoufit :o be pertinent concerning :he compara::*.e frequency of iung cancer m different population groups has &een de veloped from the analysis of cunicii ma terial. particularly surg'cal and autopsv records, supplemented to some extent bv the reooned impressions of various clini cians based upon their personal observa tions. More recently, however, attention has fumed to the systematic investiga tion of this orob'em by the same method? that have proved so successful previously in the study of communicable diseases, that i? to say. by epidemiologiai methods. Tn order to apply this method of investi gation ro the problem under discussion, we were of the opinion that a study should be pjanned so as to provide (I) a well-defined population group: (2) available data for ail memoers of this population, including the healthy as well as the ill; (3) a sample which is irulv rq?resentative of the popula tion; (4) reliable and valid observation? relating to the problem of the study. A serious defect, common to most of the studies which have been reported, is that little or no information concerning the healths* people in the group seems to have been available to the author. In order to draw a generalization regarding aJl asbe^ro* workers, it is necessa/y for a srudy to in clude living persons as well as the dead flran-- Tman ISU /V A. M. A. ARCHIVES Oh' INDUSTRIAL Hh.il TH Limiting the investigation to cases coming to autopS':, as has been frequently done in earlier studies, still further restricts its use in generalization. The problem with which we are concerned is whether asbestos miners experience more lung cancer than docs the general population. The answer necessitates the collection of reliable infor mation on asbestos miners as a group, as well as on the general population. It seems advisable to discuss the differ ences between the epidemiological approach and that used in the studies which have been reported to date. A very important consideration is the fact that lung cancer, in spite oi its increasing numbers, is still a disease of iow incidence: that is. in a given pooulatior. not many persons will contract this ?art:c*-!ar aisease This fact requires that large tunnies or grovns must be stuoied :o pro''de meaningful resuits. Recognizing tne dimculry of obtaining such large samples, most earner wruers deviated from the emdemiological method and sougnt to circumvent the requirement of observing well persons by (I) compar ing the rci&'Z't frequency or cancer in vari ous sites: (2) comparing the relative frequency oi cancer in a group of hospital* ized patients: fJ) comparing the relative frequency of cancer in a group of cases coming to autopsy. Attempting lo compare two {>opul;iiiori groups, looking only at the relative fre quency of cancer m various body sites may result in finding a higher percentage i relative frequency} in one of ihe groups, when, in fact, the mortality rate of cancer of a particular organ is exactly the same in both groups. This is- very clearly dem onstrated in the excellent article by Dorn.3 The mortality rate from a particular cause is the true measure of comparison. It is apparent that selected groups such as hospitalized patients or autopsy cases may not be in any way representative of a larger group, and that in dealing with such samples, the observer may easily find ........ of a given disease ihan would be found in mother group of the same size, bur rcprescnuu'e of die general population. It is true that investigation of cases from such a iatnple can furnish information valuable for research, but ihe use of this information m drawing generalizations is necessarily restricted. It is ihe obligation of both the investigator and of those who read hts report to make proper comparisons and to draw only those conclusions which are valid and justified. A good statistical study of cases of cancer of the lung occur ring in a group of autopsies can lead to a proper inference concerning the frequency of lung cancer among cases coming to autopsv. but only to such cases. For in formation from such a study to be pro jected :o some larger group, it is necessary that the auropsies re.rresent a good sarr.oie of that .arger groco To assume that suen is the case in any particular senes u dan gerous and likely ;o be false. There is 'ome danger that the figure< reported by some authors may be miscon strues & applying to asbestos workers or even asoesios miners, when, in fact, the authors m Question do not make this gen eralization. nor can the generalization be made for the reasons stated. Cose studv of the reports reveals that the percentages uteri relate only to the group of autopsies covered by the particular investigation. The present study, m contrast to the earlier work.;, has been planned to utilize the epidemiological method. A well-defined group of .ist>cstos miners has been estab lished in >ueh a wav that -t constitutes a good -ample uf the whole population uj -isbcsto* miner-, in Quebec. Data for ail mernber\ of this group have been collected anil analyzed. : hose concerning lung car eer have received mn<t arcful considera tion. Details of the methods emploved will he set forth later, but the tyjie of approach i- con-drlered to permit of fair comfianan* and valid generalizations. Collection and Analysis of Daea A preliminary survey ^...... ^Uicej >>l Information m February, 1956. involved dU Vot 17. /0U A*-/ S~ o >5%. /.r.v<; i-.ixi HR ix .<v/;r7viv .1 <li.>cUAiiun* wnh the physician's hi <h;nc 01 the asbestos companies |ami u-irh climci.ni>. pathologist*. rrpre-einaiivi> nf Citv-ind Provincial health dciciniiieiMami of (he Canadian Cancer Society. ami lher interested jwrsm.v It was fuumi ihat mrirbnlicv data, although -ninewhat Imnu-il. were available frnm >uch ^Hiri`e a< ilu* hospitals in Montreal .nuj Qticbev Lily, ami the 13 cancer detection centers tn the I'rnvnee. However. beciiu-< of the high murlalitv in lung cnnccr. it **vnicd ailvisahle to de|>cnil u|xm data relating to death-. The** we found lo I*.- obtamabU- at tlv 'ini stati.-'ics <letartmcni of the Minitrv of Health m Quebec Ciy. From the prehmmarv urvcv. it wa* apparent that exten sive and derided n format inn imml }>. jT'fbercd wuh re>f*ect in both the |ernn employed m the a<le<iO- minmc mdu-irv and the innr:ahiv figures lor the gum-rai l,puUiion Follow me thi- uxplnrainrv ur\c\ ihc initial i-nnrt was directed to ihc loileenon of data relating to all worker* who had been prnce-*ed through the dime at Thet* ford Mine* >nce us inception m 19^7 and similar information regarding all worker* af Asbe*tos. Que. Daw front the vlimral records includetl the age. famdv ami jvr<srui medical histone* *nuiking hahitoumber of year* of expoMirc. an e-nmaiv of weighted ex|<o*urr. ami the cour*e of the individual** health -taui* or the t.m-r of his death. From thi* information it wa- |*i*iblo to formulate a "cohort" which couid he well defined, should be representative of the whole group. and could be followed for a definite penod of time. AH of the available experience indicates that the development of asbestosis in less than five year* of ex posure must be somewhat rare. Accord ingly. the cohort was defined as in* lading evenr miner who had a total exjn*ure of five of more yars, and who was on the employment rolls in 1930 Office and other nonexposed personnel, regardless of length of employment, were not included. This uihurt wa> thu n.iluwvd by inc.nn of the jnnuol phs-wal examination record* through n -ix-year interval. 1950 ihrougn 1955. All Jala regarding this group weTc then tabulated m order to determine the characteristics of the cohort. For those who -urvivcd the enure |*eriod. reference was made :o the physical examination results and x-my findings at the end of the period. Those who had died were tabulated sepa rately. and the cause of death w* corroborates! by examination of the death certificates. A further search was made concerning those in the original cohort who remained unaccounted for when the living ami ihe known dead had been tabulated. Thev rr.-re-vnr men who had left employ'Men: through retirement or resignation. Iv.emua-iv all but a small number of these were AciMuiiicd for as either living* or dead, uni m the Utter event, the cause of death wa* suosuntiated in a similar manner, and ihc result* added tn the original list or ileatns Deatn certificate* for the Province of Queoec for the years 1952 to 1955. inclu sive. were reviewed m the department of vital statistics of the Provincial HeaJth Ministry, together with statistical sum maries of the causes of deaths in the Prov ince by counties. All case* in which death wa* certified as having been due to pri mary cancer of the iung were examined for -uch mrorm.-ition as place of residence, occupation, date of death, hospital m which Heath occurred, and whether nr nnt an autopsy was performed. Cases in which lung cancer was given as a cause of death, but ;n which it was not specified as to whether the cancer originated in the lung, were also reviewed m an effort to include all instance* of primary carcinoma of the lung m the study. The statistics for the Province of Quebec relate io population, total deaths from all causes. totaJ deaths from rtnrrr .!! and deaths from long cancer. These were collected and tabulated by counties and bv sex for the years 1950 lo 1955. inclusive. Tote* 6J9 pO \ ****** y r* T p *l' tt. .v. AHcmn.s ur ixdlstri.il Hh.ii.ru from them, death rates for the genera! population of Quebec and of individual counties were calculated for specific years and analyzed by cause. Practically ail employees of one company are covered by a group polio* of life insur* ance which, fortunaielv, nearly ail of them continue to cany when they retire. A very few are not covered by this policy, and those who leave the industry for one reason or another exceot retirement usually are no longer covered, but this is likewise a small number. As an additional check upon the information obtained from the clinical records on this group..the records of the life insurance companv were examined for all death claims paid under the policy, and particular notice was taken of the claims m which :he proof of death was basen on cancer of the lung. Deaths from lung cancer among asbestos miners were thus determined from the clinical records in the medical service of the industry and checked by means of the death certificates and insurance company records. The deaths were then verified individually by reviewing them with the physicians in charge of the medial sen-ices. In this man* ner, there was established a list of cases in which primary cancer of the lung is con sidered to have been prosed as the au*e of death. A few oses in which lung cancer is strongly suspected but not proved as the cause of death were considered scparatelv. Morralirv rates have been calculated usmg both the "proved" and the total of "proved" and "suspected" ases dunng the years un der observation. Comparisons were then made benvevn the death rates from the same cause among specific segments of unex;osed persons. All lung cancer deaths, both suspected and proved, were carefullv ana lyzed to determine possible relationship or correlations between the development of lung cancer and any factor known from the clinical records, such as famtiv historv of cancer, [personal history of heaw smoking, .w^oience 01 asbestosis, or expo<ure to asbestos. 640 In addition 10 this analysis of deaths oc curring m the cohort and during the years under observation, e'er.* known death from cancer of the iung. as well as every case diagnosed but still living, has been tabulated and analyzed. Thev wnl be discussed separ ately from those included m the population and time-interval under study. A comparison of lung cancer mortality in the asbestos-producing counties has been made with that in counties which are far removed from the asbestos mines and m which, presumably, no asbestos miners live. Finnilv. in order 10 broaden the compari son nf death rates m dinerent population groups, the rates have been collected for C.iiuda generally, arm for the Lotted States, according jo tre rrc: -rcent puolt>hed and imniiolisned material Results and Interpretation The Conor: which was constructed accord ing :o the criteria described in the preceding .-ecnon has been conquered individually and compared with ihe general population. Description of the cohort will be presented here as a preface to the results of the study: OfiritKi <_'**** Pti-mtt Lh*. Finit' CArt - i9|| )V*4 b* I?1J Ct*rt* ( iwi*i ihiwf raww* *.1 -n.rf.ll ' lnr 4.091 m j.mi IJT1 117 4 -.473 l-8i :o Tables I. 2. .V and * present age. number of \ears of employment. weigh ed avenge cxinsurc. and .inokmg habits of the cohort. A comparison of the exposure tu asbestos 'lust i> presented in Table 3. All members nf ihe vohort were placed in one of three categories, representing increasing degrees of exjosure based mi a weighted avenge < the years jent at various levels of lustiness. The degree ( du<imess for each job category was determined a^'er -p--- lion vvith jicrsons familiar with the environ ment and comliimn* in the various work r./ IT. iuv, /VM f*/ 7 J.0 i i I LUXC CANCER tS MIXER* TaJll \.--Xmmbfr <**4 Percentage Distrtbvturm Ta>lc 2.--.ViArr and Prrer^toor D'Unktiti* by by Age L/xAtb ot Ei"Pioy~>mt Ar* T..l. A*r*S* ............................... .................... VuSM ) ' *>u: iui J.1%* * Ua IR0 0%. Prf G*M 4 mit % 1Q0 Ltneift of CapWrlMlU l*V-#1*................... ~71........ -Jt................ A muiTrouunts.o.i..i.a...o..o...^..*..*..t.u............. NuoBti iL.-rTii rau m u 1.15I4I Pv G"i 0 I 10 i i 100 areas. For the pun*3**5 01 calculation, the assumption has bent made that the relation* ship between these categories is linear, and that Category II is twice as dusty, and Category JIT three times as dusty as Cate gory I. uaJly smoking more than five cigarer.es per day. Persons who smoke pipes or agars exclusively were not considered to be smok ers for the purpose of ibis study. Table 5 presents Lhe yea--oy-year ex perience oi the cohort and indicates tne Tajik X---Sumer* ana Percentage Jtj/njyiww Espcrutf Caieytprx T*tLC J --iVumo/* and Percentage JlffrOu/vw T: J"*01*9 r.iOitt CE i nufauir<r Ut............ . in....... OaiMom. Tun....... Axnn LioetuR, vMroho* :.ui : :so i.r:> 1154 JO rf C401 34 ja jo :00 S atelier tUOiu Ssottn .............................. Nooinjoirn.................................. OlUMv................................................. Taul _ Nusmt i.in iju 33 ftt Cn< :i :i 100 * Lm iiu a_sr*. The fourth variable, smoking habits, was similarly tabulated and >s shown in Table 4. This was included because the informa tion was available and because smoking was regarded as one of the variable* which, besides the environment, could conceivably influence the development of lung cancer. As used in this presentation, the term smoker refers to a cigarette smoker, habit* number of deaths each year from specified causes. In general, a case was considered to be "proved'* as one oi primary cancer of the lung when the records showed that the diagnosis had been supported by an autopsy or surgical resection of the lung with microscopic examination of the re moved tissue. In one ase so considered, however, diagnosis was confirmed by bron- Tajix S.-- Year-byY tor jpe*\entt oi Cohort and Drtub Patet per IQODOQ Mam-Ye^t of Ptsk No. Hi** At btlOAiH - Vox- mi..... II1Mt*AM1I ........ .... tut..... mi 1.1*3 irr I.IU 344 3J10 Tetxu_______ "^1 i 1 o<~ m iin tui'ivi o4 ra> Fnrenr C*. 04 Uin Cum at Ouii Sutomod FnArT Ca. m Uin| Otter Cnwoi 1t1; r 44 s 44 XU tJutnov* Mot(o.MVafcon 1 VO i U3 1.IU3 iPbki vrj UJTU --1 ptr ittA* A*-oer 4 rat 344 3ro\ f4t 1 ** .V. A. APCHft'E.'i or tXDL'STXlAL HEALTH TaIlX 6.--"P'r,ed" Casfi of Penary Confer or the L**9 Cam >. All W Saetiir Y 1 CS r* va Vo Yo Ya Ytt Zipmur* 2* ' Co. 1| H >t m Cai. 1 ) >1. m C*t. 1 H yr. iQ Ca. 1 sr it Ctt. a Urr ifl Co. in X yr. Ifl Cal a is rr. la Cu. I ar.u Cac uu DM >. J-O a n-ra-u - >>* >. -u Yn '-o YM 1 * Brancit. ueii8m Vo 'a No choscopv with visualization and biopsy. In another, although there was no autopsy, the diagnosis of primary cancer oi the lung seems to nave been beyond question. The term "suspected'* primary cancer o: the lung was applied to those cases in which the diagnosis remains in doubt but some ot tr.e evidence points to cancer ot the lung. There were three such cases The term "man-years ot risk " has been used to mean the namber ot men at risk for the year under observation. A person who lived throughout the year was counted as a full mo.n-'.ear oi risk, bur one who diet! during the year was counted as one-half a man-year. Deaths occurring in the cohort, and m which lung cancer is considered to have been proved as a cause, are shown in Table 6. In Tabic 7 are shown three deaths which have been considered as "suspected" lung cancer cases. An indication of the importance of these "suspected" cases in interpreting the results of the calculations is desirable before fur ther discussion of the mortality rates which are derived in later tables. For example, it happens that the rate found for the proved cases is close to the "expected" rate based on the general population figures for the Province, as will be shown later, and on this basis we should find eight deaths frnm lung cancer among the cohort. Actually, nine cases were observed. If, however, the 3 additional "suspected" cases were in cluded, increasing this figure to 12, the total would be very close to the 95To level of significance. However, having found just 12 cases, we are not above this level, and therefore the hypothesis that asbestos miner? do not have a higher mortality from ;ang cancer than does the general population can not be rejected. Nevertneless. the occur rence of 12 cases in this sampie would ncrease the 'ate to a poir.: which aoprcac.ies the significant :<ve. Because of the tremencous importance of the quesncnaole cases m this respect, some detaii regarding ihem will be given here. In one of these cases, the suso'C-.on of cancer of the lur.g is based upon the x-rav interpretation, and. although no autoosv <*35 performed, the death certificate indicate? that death was due to lung cancer. It 1? well known that the x-ray appearance of fibrosis, especially it a localized density or a superimposed tuberculous lesion >$ pres ent. can simulate that of a tumor, and by itself, does not lu.Mify the inclusion of this case as nne of "proved" cancer of the lung A second ca>e was certified a? has mg dieu bv reason of hydrotnorax. possibly due to lung cancer, but again (here na-* no surgery and no jiostmortem examination In the third cn>c, although it was subjected to autopsy, two pathologists disagreed as to whether iung cancer was present. The death was certified as having been due to chrome myocarditis with nephritis and pulmonarv congestion. and possibly cancer of the lung On the basis of these facts, it seems unwar ranted to include these three crises among Tai_z ?.--mS*steettdm Prin^rw Confer of the L<mg CmM. r 1 I 6*2 An U lwr r* r*. Ta CipBM* n rr. m c*c ill UF.inCiUll tarr. .0 C**. a PM - -U *--0 A0ir v* v So Aitaao y Yr N* Vol 17, }\mr JO M .Vt. C'.I.Vt 't.R IA .fVW/'s7'OV M/Vi.R S "proved" iiisitinio of lung ciiiiot On tin.i.ther hand. they cjiiikk. in fairncx be dis regarded completely. It is fur thu rea-on ihai mortality rates hav* hern ralcunied I a It In way*. Tabic 8 jive* the rates by age groupThe rates by length of employment arc shown m Table 9. During the first 40 vears nf employment. the rate rises, an observanon which seems plausible since the men were growing older. However, after 40 vears of exposure there are no "proved" rejioned for a toui of 240 men dur ing the six years, or about 1440 man-years of exposure. When the "suspcxied" cases .ire ruined, one case does show uu m this T.sm.c S-- L*q Cancer Death* trv Aye Gfjne r T'u ' --Lw" t_ ucr Dean bv Uytn l r*' v-t l*-t*___ 7U-?.... *) TjL*JI .. . . \* ^ rinoai i :v IfXcli 1.1 Lw Or*tH. --------V-'f-l--w-I----------" oul Annwai t^inc OtiaiaaSrwairf** fr 100.000 r.mmar11n1 i'i Tm* >-*................... !ivi.......................................................... 3V7S................................... ift-lt................................... ............... 0 :Vn* 9 3 : W !U 1*3 U' 1* Annual t-jn< Cancrr Driih Sii i<r 104.000 Man 1 r Cttwfwrr Aft nUB Jfr-........ *U>--w..... |-fB*1 aINi :u T*l*1 Mkl xAn U*tr >iil .................................. SI J* period. This would produce a rite of 69 l<r lOO.UTXJ. again demonstrating the ttv lionance of these rjuc>tcmable. but un proved. cases to the final conclusion, iierausj. it there were no cases n this number of men with long exjmsure, and if asbestos is a carcinogenic agem. it muM be concluded that these 240 men have demon strated considerable resistance. This is a bio logical phenomenon which has been observed prexiouilv and ts consistent with the theory of an intrinsic or endogenous factor m can cer. The only other explanation would be that the <uscepubie members of this age group had died earlier of lung cancer. Table J8 which ^ope-ars later in ihi* -cciton. m* yrrtmm-- i dicates tn.it the members of the enhurt did not die from lung cancer at a sounger ige ih.m :ne general population. The rues by weighted exposure are shown in Tjble 10, and it udi be noted that thev present strong evidence against asbestos being a carcinogenic a^mt, for. if exposure to asoestos is m any way con nected to lung cancer, we wouid expect that the longer and heavier the exposure, the higher the rate that wouid be found. The only possible error m this interpretation muld occur if the weighted exposures were inversely related to years of emplovTnent, Tami iO-- (.n**t inmr.r Death/ Jv F.jfatuer L ate jo?" Numwt < rtl4U* Clitcir' II ................. Ulimt m................................. MVi Xunrt t Lut Ctnccr D*iiM V Ol O-toaj i rwi*1 I-.. Y ru 9ai 7031 4 Ti.rI rvoi ]j ii u* t Aivnutl l-amr Cr* 0*lA Rjllt |f >00.000 Mo-w.r 1 4i LipMur* Cji4cr I ............ II ........................... .................. Ill ................................... U(M*V..................................... ... .. 0* ul......................... Pf*40 It t ri i: * i* *Ai ! i i / ` 7'"'-i 3 I A. If. A. ARCHIVES OF ISOUSTRIAL HEALTH T**ir 11 --of Pfr roJ in KoflOHJ Weighted Eiposurr Categories Oy Ltnql/ oj Empto\-mtnt L#*n -- Ei*r"< "ai*n*i3 E mun U jitrortri i It in Xl*M-.l3%9 JO>--J* 30* MT. IJKO;l vM:miku: <0 17ij90r1 41 51 10 A wT-vout tfstin ~Ut OtiOBiun l'J ::jo i.rr: !7J 1*0 t>- tiw* a 33 Tout 3.3m91 603 U i.tsa ITJ in which case the heaviest weighted ex posure (Category HI) would show the shortest length of employment. Table II. which lists tne number of persons m various exposure categories by length of employ ment indicates that this error has not oc curred. In fact, the avenge number of vears of emmoyrrent tor eac.n exposure category is almost identical. Taole 12. which de'-eiops the rates for smokers and nonsnokers. is most striking. It shows that not a single case of lung cancer deveicoed among the 1265 nonsmokers and trut ail cases of lung cancer, both "proves" and "suspected." occurred in smokers. Table 12 was so striking that it was felt that further verification was necessary. It was possible that some abnormal distribu tion may have occurred, e. g.. the non- TaolI I.J.-- tV*iibrr oj*d Percentage Distribution of S"toke*j ana imsmoerrt ov Age Crones A it Cf*Wt 9--4 40>................... U44. ............................ U-- OftlfW**...................... Tu_____ AMndKt........... SMiff ixn IM 411 164 J crj nj NtmiMiir * tf4 305 1)0 ij* *4. CiKrwm 13 X40.; TsCL 12 -- <lw*0 Canrtr Dtaik foe Jna .Vonimotees Vumoff at Pi S..r.o...r..n.............................. Uinn.................. Ttuli......... Mini; HalHt .iLl any Cuxf 14iai N ( OvaiM I'arton* Taut `l-J&S * U8 m10 !. 1 13 Annual L*nc Ci-iff 3*m *iii ser 100 OOO MmA'itn oi jlir^iuff 3* Hi6i ^4. at Dcatnt Pw*w 74Ui ScnaKm....... ............................................ \anmotan U n * no -0................................................. n 0 9 *3 9 9 0**r-4ii................................... S3 * smokers may rave 'r.ciuued a larger percentage ct young-ne:i. Con-eouently aoditional Taoies 15. U. and 15 were con structed to show *he distribution of smokers and nonsmokers by age. length of emotoyment. and degree of exoo?ure Althougn there are sugn: cttcerences they do not account tor tne tac: that ail observed case* of lung cancer were in smok-ers. In resoecr to age (Table 13) the combined average age of the smokers was 4 9 years less tnan that of the nonsmokers. Table 14 show* that as far as lengtn of employment ts eon* Tholc 14 -- VwmAf** and Pereemoo* Distnbnii.'n of 5oi.ic.-r/ 3* \'anjtooett ov Length of 'nfio\-ment U-*th Z B9*HTO4<H J?O>*)*?.... Taun......... A**m4 won* a* iB3`rtt4"i______ Nuawr Vntni4ri 40* jr .M7 134 Untno*rn 19 U no S3 I in 1*0 rm ijiv 4 o 9 x i r ft iij 13 9 Prr*au* Owi0at Ai Orw* SMltr Nontmoc** JO--4................................ 0-14............................. 1>*4................................ * ............................ Unrno--i.................... HI tIJ 11 S4j i: : 1n9 0 J a0 Tut............. im**, lC, CMnovw *0 0 xo 10 0 30 1.0 l% * ikn % ej. at Caeior^ntflc 3-4 .............. 10-K .................. *J0................ 30->4................. 4^-4........ 3fr+................ Touu .. pf*i*i4Lif Oa*nM(M ViHineirr *1J u; is.: ii i ij 1*% t'nkfwvn X0 60 l**. LLWG CANCER IN ASBESTOS MINERS Tajle IS.--b**mbtr o*d Percentage Ditteibui*on of Smoktrj Nonsmokrr/ by Exposure Category Etwiun C**Mt*TT r................................... u................................... LU................................... Uum*u............. TouU_______ a'tfVitrpnn mm*mt...................... Nuabai ScMKdi NtniMitn list I.MI 4.01 02 a i .en IJU u ij Uum*k * t 0 SO SJ Pctvbui* Dairl&uttsa Ciwnn t................................... II................................... IV................................... ................... IcMtin sj *2 lOi 0.1 iao? Ntuatitn ra u.; 2t.r 0.1 ir. UaEiMva SO u.o U0 0.0 100% cemed, the smokers had worked about 2.3 years less on ihe average man the nonsmokers. Wim longer exposure and greater age. one would expect the nonsmoking group to show 4 higher rate it lung cancer were due to asbestos. Table 15 shows that the average exoosure category was almost the same tor the two groups. Therefore, this vanaoie seems to be of no importance in accounting for this difference. The result of this additional analysis is that none of these factors appears to lessen the effect of Table 12. Companion of the Cohort Experience with that of the Province of Quebec, Do minion of Canada, and the United States.-- In order to make a comparison of the experience among asbestos miners with that of the general population of the Province of Quebec, statistics were gathered, as stated earlier, in the office of the Division of Demography in the Provincial Mimstrv of Health. The dau on iota! deaths, deaths from all forms of cancer, and deaths from cancer of the lung were obtained by sex and by county for the years 1950 througn 1955. In addition, all death certificates which specified primary cancer of the lung, and ail those which indicated lung cancer but did not specify the origin, were exam ined for the years 1952 through 1955. Table 16 gives a tabulation of the number of deaths from lung cancer in the Province and in the cohort lor the years 1950 through 1953, and shows the annual rate per 100.000 in these segments. It wiil be noted from the table that the mortality rate for the "proved'* cases m the cohort is oniv slightly higner than the rate for the Province. When '.he "suspected" cases are included :r. tne calculation. :ne rate tor the conorr rises to 53 S per 100 000. which is aoout 50^2 higher than the race'for the Province. This, it will be recalled from the previous dis cussion of the effect of the "susneefed" cases cn the results, approacnes but doe; not exceed the significant Jevei. One further interesting observation from Table 16 is the rather marked increase m the total number of cases for the Province between 1950 and 1955. It is assumed that at leasr part of this increase is due to rmproved recognition and reporting of lung cancer during the interval. For this reason, the years 1954 and 1955 were thought to be more nearly representative of actual condi tions. Even so, it is quite likely that the general population is not studied for lung cancer with the same diligence with which (f trhMlfil Ml Taju 16.--Comfiaruo* of Cohort antk Provm<t of Quebec NuiSBv* . ii.' Laos Carm? OwB* ?inMJ lUO IBil IU2 tU) its* tUi i.iMaoe* i.m i s.itLoaa m it to wan si 9 1I w aa U7 3) is* T*uu I.Ut 13I i.m \itnoal Xft't art 100X00 rj us a_j U If* rf**1D<T AfQWI K h*l ISUM 111 ** lull* tMint In 'o. . r*. .. * itp^noau gitoiidiiaAttauBV'iiM obo^uim moi1* >. iUI. * ibtnuaut** paeui*<a* `or itt* l>ume*r *li** t rah#rt it * l?JX Oif * U 0- / 2. b 4 ! A M. A. ARCHIVES OF IS0US7RIAL HEALTH TaU 17--L9 Conttr Dtgtbt fo* Ikf ?*<rs\n<t of Q*.`bte lt C*gn to-** IV Touls r*ouut>on m 3C.JUJ ir.AU LS7.000 Sunt** *< D**u Tout CmiM 7ei*J IT 7 too III ii i* is 13 as IZD Sarei6*o ?trar Tatil It 1 oa it i: tt 9 191 w lU Taui Cmt4 j prciOad frjo.1-. Tout rf**o T*Ui rr*d i 17 t to 31 M sr nt 7s1r ia M ia M MI U1 337 III i Dot* Ltta prr 100.000 1M llil Tout! CmiCid ScciAm Tout Cm;i*d SoS* ^*=rr A Oim# **........................................... o-st........................ _..................... sa-*a................................................ **-................................................. o*tr<u................................... T*ul ;* uj no I-- r uj Toni Ppv*m To<*< ?t***4 TUI Pro*d i.r i i it j 7U i nr r* so ai u rJ so-- :o u 12 it j rr: Mr * -r.3 iji u.t * * m n rt 'ti r.: i;- ' D*iu t**o (ut.i ar'Jovi id ' NCipimpnosnu. >/o*'*r-:rui iiti-wotootonuo.mntti.o* 93'T<at itii ?'oumi <or ( c~run for aim it iat wai osouitm nr ia**. u i*n this disease is looked for in the miners. and This comoanson. summarized in Taoie it seems probable that the mortality rates IS. shows true the ooserveo numoer of :or the Province mjv be low This would deaths m our samoie is not significantly appear to be substantiated by the fact that greater than tne exoected nurr.oer of deaths, the reporting ot ases m -he cohort showed based on the average of the 195-1 and 1955 no sucn increase over the same period. figures for the Province. It is true that, in Table 17 was compiled to show the an the case of the age group of 65 and over, nual age-specinc lung cancer rate of cases the five deaths provide a figure which is in which the death certificate merely read almost significant at the 95^0 level. How "cancer of the lung.'* as disnnguisned from ever. it should be noted that this number those <n which the diagnosis was confirmed includes one of the suspected but unproved by autoosy, surgery, or biopsy. The term "specified primary" refers to those cases m these ru'O categories m which the tumor was specified as having originated m the lung, ft will be noted that, of the total cases reported in 1955. a much higher percentage cases previously referred to. rurthermore. it is rather likely that the rate for the general population is understated in this age grouo tor the obvious reason that the exact cause of death m the very old is not than in 1954 were specified as primary. The table also shows that a higher percentage T*atc '8 ---Co^teruon of the Atu^i o*4 Ej;tttri .Vitmorr ot Confer I i of the total cases certified in 1955 were proved, again indicating increasing interest Dreikt by Aft Among Atbrvos Minert in this disease. A comparison has been made berween the age-specific rates shown in Table 17. and those for the cohort, shown in Table 6. An average of the 1954 and 1955 rates for the Province has been used, since the 1955 tn OfVUB Ti*J rv*<A*0 Pnnif* A*>* 9>r iQD OCO O-M V%* S3-** liatn**-* 1J c nj Obw i'* t S*. V* *4 Erva****'*4 i Diiiti Mmm Dm<U ` frt**o Ttui I mi um:i m 1 1 1 t 11 t 1I t 4l 9 figure was higher and mav have been ex ceptional. fumeri * **'p4 I *'*#* ( (h* it>* III} ttt tomtit t *iuaiiT <0* in* i QhOh. * bM Vol 17, Jtme. I9H /3 I I LLW'C CAS'CER IS ASBESTOS MISERS Tail* 19-- Aar Dittnbv/fon of Adult Moiti for Tahlc 20 ~~ Annual Death Rotei per ICftfOO f.-r the premier or Q**bre. 1951 * Cjmtrr or the L**V " Canada # A| Gnus TmaI______ I U.4> in Conors M 19 10 I I * Support. 1104. a matter of the same intensity of interest as it is in younger persons. Table 18 also answers a question pre viously raised. It shows that the members of the cohort have nor died from lung can cer at an age earlier than the general popu lation. and that such an explanation cannot be onered for the absence of lung cancer in 240 men with more than -*0 vears ot empio> mer.: re'trreo to on page 6-3 Before ;tavmg this comparison of the Province with the miners, it should be shown that their age distributions are rea sonably the same. That this is the case can be observed from Table 19. It shouic be remembered that the miners retire and consequently, it can be expected that the oldest age gToup will be larger in the general population. The data presented in Table 20 indicate that the lung cancer rate generally decreases after age *0 There fore. we could expect the rate for ail people over 65 to be smaller than the rate for the group between 65 and 75. which would apply to the oldest group of miners. It is felt that by using the whole adult male popuianon. we have developed rates for the gen eral population which are somewnai 'ower than if we had been able to exclude the people in the general population over 73. A comparison between the asbestos miners and the population of the Dominion as a whole was made, using statistical maternal from several sources. In one source. Phil lips '* gave age- and sex-specific rates for Canada for three periods between 1931 and 1952. The rates for males are g>en in Table 20. These figures shew- strikingly the increase in rates between 1931 and 1932. and this Art G'vuo Um* 30 IVa 1>J9 v* 0--9 AUk au Am Onun o< Tnn ;**l -1*0 0: 9ft :j i J jji s. J i : i7 s it : u !.* r: ii2a.jri ara.i *-:i i.u u j ie* 10 T 3D I MJ 111 30 S 0 9 *2 : M.: u mi no :j i.i ji * "Muroiii* Uuxs m Cjrwia. ' 1411 io i*SJ- mcrease is particularly marked after age SO. confirming an observation pre'iousiy made, io the enect that until recently lung cancer has probably been underdiagnosed m the eder age grouns m the general 'ecuiation. To use these figures for purposes ot conicanscn. it is necessary to combine me rates for certain age groups m orcer to conform, to the age distributions used ;n this study Since the exact populations m eacn age grour. for the years indicates ;s not known, tms must be an aooroxirr.aticn. However, the rates would be somewnai as follow*: Aft Cm ;o-<* H iS-44 iS* 1 99 fl *J These rates are, in general, lower than those des eloped for the totai (proved and susoected) cases of lung cancer among the asbestos miners. The only large dtnerencc. however, is in the age group oi 65 vears and over, and >t is quite possible that the rate for this group may ha\e increased for Canaria between 1932 and 1954 as u did for the Frounce-of Quebec i Table 173. A further comparison has been made \nh an o\er-alI rate obtained from the American Cancer Society for respiratory cancer death* m Canada m 1953. This rate, tor males, is 20 S i>er 100.000, or 5 more per 100.COO than Phillips' 1950-1952 rate, and compares with fc. .... ,jruved ca<es and 53 3 per 100.000 for lotal cases among :he A .1/. A ARC HU TTY Of ISDCSTRlAL HEALTH T.^juC 21-- Vw6er t Deaths and Death Rotes /. 100.(0* hr Aoe G'*mfs joe the Adult Mole PoruiOt'3* ihe U**ted States* Ac* Crau} U-C4 <J-r Taul Hpuoi** :<.x l# *s I.JVIIUJ j.*ra.joo M.tlt.OOD Cun liutf* lUtt Otr 100 003 LS at ni no ra 0*u (is "Vuaj Suia *l to* Cntt4 Suml " vi. i M !. IU1 asbestos miners in this study. It is there fore obvious that there are no important differences berween the rates for asbestos miners and those tor the general population of Quebec and the Dominion of Canada. Since it is probable that figures for the United States are more complete and. there fore. possibiv more comparable to the data for the miners, age-soecinc rates -.vere com puted from 'V'ital Statistics of the United States.'1 Y'olum.es 1 and IT. for 1952. These rates have been tabulated m Table 21. It is apparent that these rates comoare favorably nn those tor the asbestos miners as shown in Table S. Still other rates tor the Untied States were obtained from the American Cancer Society, and for males, these were 25.3 per 100,000 m 19:3, and 2S 0 per 100.000 m 1955. Thev are nor identical with the rate calculated from the figures of the once of Vital Statistics, but this i? possibly because the American Can cer Society rates are for males of ail ages. Nevertheless, they too. compare favorably with the rate? of 25 <or 3-4 for toral cases) obtaining among the asbestos miners. Turning for a moment to a comparison benvetn the asbestos miners and persons who are exposed to asbestos in one form nr another fas distinguished from the gen eral population groups fust discused. who have no exposure) an interesting ooservalion can be developed by deduction. Hueper has stated that there are about 33.000 f*r?ons exposed in the United States, and we haie found that the Canadian mines employ about 8000. Elsewhere, it has been estimated that the workers in England who have exposure total berween 3000 and 5000. With workers in Africa. Denmark, Nor- wav, and other countries, at least 30,000 person's must be exposed throughout the "oriej. and u can be assumed that tins number hns been fairly constant m the 20 vears since 1933 when the first case ot asbestosis with lung cancer was reported. At least 1.000.000 man-years of exposure has thus been accumulated, and this figure can be divided by the approximately 150 cases of lung cancer with asbestosis re ported during the 20-year period. This gives a rate of \5 per \C0.QC0, which is at least indicative that any lung cancer rate which can be calculated for workers ex posed to asbestos dust is not much greater than that for the une.xposed population. Comparison Ser+cen Eight Counties Ad- ;0Cni to the Asbt'SioS'ProOucxna A'tQJ ond -E.:r.: S<.\r:; C:unt\*j--To compare iurg cancer mortality *a:es in the counties surrounamg :he asbestas-prooucing areas with another group of counties in wmch no as bestos miners are liken* to reside, the rates were comouied on the basis of figures for ihe years 1950 througn 1955. The e*gir counties selected for comparison were Argenreuti. Chateaugay. Montmarny, Portneuf. Eichlieu. Riviere-du-Loup. Sc. Hyacmthe. and Terrebonne, mamlv because they represent a wide geographic dtstnourion througnour the Province. The counties selected because of their proximity to the asbestos mine? include Arthabaska. Beauce. Drummond. Fromenac. Megintic. Rich mond. Sherorooke. and Wolfe. Table 22 shows the number of lung cancer deaths for th- years 19:0 through 1953 for each of these counties, and a mortality rate, based on the adult male population in 1932. To emphasize the comparison, Megintic County has been shown separately, a$ has the Province of Quebec and also the Prov ince with the eight "asbestos-producing" cuunnes subtracted. Because of its unique lung cancer death rate. Montreal et Isle de Jesus has also been listed in order to provide further comparison. It is apprcm .uim me taote that the lung cancer death rate for the eignt counties 64j Voi 17, /w J95i l i i i LL'XG C.4XCER IX ASBESTOS MIXERS Table 22.--Xnmofr of L**o Can<rr Deaths o*d Hair 9** IQQOOO Man-Yearj Csust*i Xfotmoe EjIOi "Adiwvm Couaitvt Etrst Mtanan CouotiM QiMW Pre<o OuBr ! H6l ' MtMvat" suntift MBUW oi (in a *mi Mk Lun C'A<^' OtlMAi ' V<9oJt Mi* . Pooumwn m? :i90 IJ1 !SJ1 HU I1M 13: ICO mo UOU) t.IVCOJO J 1i i J1 : m to =0 JO) 1,100000 io n? ru jw.ooo i ? ijj Tolu R> r*. ioQOOO h1 11 r1 n1 * It itt u Qla lune obov 4muu oaeerrvd *<ur * . t immediately surrounding the asbestos-pro* duemg areas is practically identical with that of eight counties selected for comcarison. Whiie Megantic County has a rate nearly twice that of the combined eight selected counties, :t is lower than the rate for the Province, and considerably lower than '-he rate for Montreal. The figure for Montreal would certain:y be higner 4xceot ter the very low numoers of deatns reoortec for 1950 and 1951. and it wouid appear that in tnose years some error m reporting has undoubtedly been made. On the basis of the other years. 1950 and 1951 deaths would be expected to be aoout 200 greater This would result in a rate 01 -0 per 100.000. The only possible conclusion from this comparison is that there is no evidence that the persons who live and work m the coun ties surrounding and adiacent to the as bestos-producing areas have any greater incidence of lung cancer than those who live elsewhere in the Province. Coniineon All Recorded Luna Cancer Cats, L.\~mg and Dead, asnontf the Asbes tos M'mtrs --Although a simple enumera tion of all the known or susnccied ca*es of cancer of the lung in these areas has no particular value from a statistical pom: of view, it is of interest to summarize such cases for the record. There were nine deaths prior 10 the beginning of the time period covered bv the sturlv. including one in which the diagnosis was mediastinal lymphosar coma. During the period covered by this invfA-Tgition, there were nine proved cases and three suspected cases in the cohort. Through 1956 and to date in 1957, there were eight deaths, six of which were merely suggestive of cancer of the lung and in cluded such diagnoses as mediastinal < lympnosarcoma. mesotheimma, cancer of the v* leg with nietastases to lung, abscess of iung. and cancer of the pancreas. One other was diagnosed on the basis of x-rav oniv In addition, there are now living four cases m which the diagnostic evidence is strongtv suggestive or lung cancer. This is a total of -5 cases of all types, including 10 "sus pected" but unoroved cases, and s that are still living. The remaining 19 constitute the local of proved cases of cancer of the lung among 1 he asbestos miners since !?40. The proved cases averaged 59 years of age at death, and vaned berween 37 \ears and 68 years. Thetr working span covered periods varying from a minimum of 14 years to a maximum of 37 years. OnU three men had loss than 25 years of em ployment in the industry. Seven among those cn whom such information is avail able had a weighted exposure placing them in Category III, and six worked in an exposure represented by Category I. There were only 17 among these prosed lung cancer cases in uhich we have in formation regarding the presence of abestosis. Asbestosis was present m ntne, although it was minimal in rwo. Two path ologists disagreed regarding its presence m another At least seven of the 19 proved lung cancers, therefore, were not accom panied by asbestosis. Summary and Conclusions [merest in tne question of whether there may be an association between lung cancer Draw*--* Trmom 649 / ^ 7^-c-O f A. A. ARCHIVES OF INDUSTRIAL HEALTH and exposure to asbestos has been evident since the report m 1935 by Lynch ana Smith of a case in which lung cancer and asbestosis were both present. As additional cases in which the two diseases coexisted were reported, a causal association appears to have been gradually accepted by many authors, although some workers considered the correlation to be inconclusive. The pres ent studv was undertaken in an effort to de termine whether a ausal relationship did, in fact, exist between exposure to asbestos and cancer of the lung. Since most eariier studies had been limited to enumerating the lung cancers found in certain selected samples, such as cases coming to autoosy or deatn certificates in which asoesiosis was mentioned, it was apparent that they couid not fulfii! the re quirements of an epidemioiorcal ana sta tistical approach to the problem The present study was. therefore, designed to meet the reauirements of this method. After a prelimmarv survey to exolore the availabilirv of reiiaoie information, data were gathered on workers in the asbestos mines in Quebec, based on their medical records. A cohort was defined as a group of asbestos miners having at least five years of exposure and who were in the industry in 1950 Data relative to their characteristics were collected and their status at the end of a six-year period of observation was de termined. In the case of those who had died, an exhaustive search oi death certif icates and insurance records was carried out in order to determine as nearly as possible the exact cause of death. Mortality rates from lung cancer for the general population of the Province of Quebec and its various counties and for the Dominion of Canada, as well as the United States were calculated from statistics collected in the appropriate places. Comparisons of the rates obtained for asbestos workers and for the other popu lation groups were made according to ac cepted statistical methods. Records were obtained on 6091 persons who fulfilled the criteria of the cohort. It was not possible to trace 133 of these for the whole period, but 5771 of the remaining 5958 were found to be still living m 195: or later. Of the IS7 known dead, cancer of the lung was considered to have been rasonablv proved in 9 and to be strongly suggested in 3. The members of the cohort were studied with respect to age, length of employment, a weighted average of their exposure, and their smoking habits. It was found that 4675 were smokers within the definition o: that term as used in this study. Thirty-four per cent of the cohort were more than *1 years of age. and thirty per cent had beer, employed for longer than 20 years. Thum per cent had a weighted exposure whic.r placed them in the category of highest ex posure. The mortality rate for lung cancer. i computed on the basis of nine "proves" deaths among the cohort was 25.3 per ICO.000. When :ne three "susoected" cases wer? added, the "total" rate for the conor. rose to 53.S. The importance of the susoectes but unproved cases in determining these rates has been reiterated because it is likely that such cases would not be included ;n (he statistics for the general population and because they influence the results so mark edly. According to the findings in this study, the mortality rate from lung cancer does not appear io increase with length of ex posure or with degree of exposure, a fact which presents strong evidence against the carcinogenicity of asbestos. Comparison of the experience among the asbestos miners with that of various seg ments of the unexposed, comparable popu lation shows that the observed number of deaths among the miners is not signincanrly greater than the expected number. The rate for proved eases among the asbestos miners (25.3 per 100.000) compares well with the rate of 22.5 per 100 000 for the rest of the Proving* --i 2?? 100.000 for adult males throughout the Dominion of Canada. It al>o compares satisfactorily with rare* 650 Vq\ 17, }*+e }9'X A*/ /7 LL'XC C.iXCER IX .iSBESTOS MIXERS of 3/ .2, 25. J. and 23.0 obtained f rom \ a nous sources for aduli males in the United Spates. Finally, m this matter oi comparison, u would appear that the world-wide experience of persons exposed to asbestos dust is not worse with respect to lung cancer than that of the unexoosed population. The counties surrounding the asbestosproducing areas, in whicn it is presumed most of the asbestos miners live, have al most identical mortality rates with those of eight counties "ideiy scattered through the Province, and are lower than those tor the remainder of the Province, and much iower than the rate tor Montreal. Since 19-*0 there have been 19 cases in which the diagno*is of primary cancer of the lung :nav be considered to Have been proved. 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