Document VYkgxnEL4nLxJogYQeaZrbXw

FILE NAME: Asbestos Mining (ASMI) DATE: 1950 DOC#: ASMI025 DOCUMENT DESCRIPTION: Unpublished Conference Presentation on Pulmonary Cancer in the Asbestos Industry /r MR. CHAIRMAN AND MEMBERS OF THE SYMPOSIUM. I was asked to present a paper on the topic Pulmonary Cancer in the Asbestos Industry, net on account of any special qualifications but because I happen to be in charge of a Clinic which has as its primary function the supervision of the pulmonary condition of some 4,000 asbestos miners; such a group of employees working in a small radius of 5 miles offers an exceptional oppor tunity to study the problem of cance.r of the lung in relation to the inhalation of asbestos fibers. PRELIMINARY REMARKS. This question of pulmonary cancer among the asbestos workers is as confusing and obscure as the etiology and the patho- genicitv of cancer in general. From 1920 - 1950 the medical liter ature reports a series of 5$ cases of pulmonary cancer and asbestosi Obviously this list must be incomplete but, nevertheless, one cculc ask is it sound to think that the mere fact of detecting a total - of 5& cases of pulmonary'- cancer during a period of 30 years is sufficient to establish a causal relationship when one realizes that in 1950 an estimated number of 45,000 men were employed in ' the asbestos industry, and that during that period a minimum of : 100,000 employees have inhaled a significant amount of asbestos g dust? It is recognized that the English statistics publishec .. in the Annual Report of the Chief Inspector of factories for the year 1917 seem to indicate a causal relationship between the factor asbestos and pulmonar*}' cancer but, on the other hand, in South Africa with about the sane number of asbestos workers as in Great Britain, and when there is also a large number of autopsies and good medical control of all employees in dusty trades, the statistics do not indicate any abnormal incidence of pulmonary cancer. If the frequency of pulmonary cancer in South Africa and in the Province of wuebec is really not higher amongst the asbestos workers" than in any comparable groups as it seems to be, is it possible to suspect that the asbestos mining industry might be different from the Asbestos Textile Industry as far as carcino genic activity of the asbestos is concerned? The fact that the frequency among the 3G jG00 asbestos workers of tne United States who are also working in the Asbestos Textile industry is not unown to be higher, adds still more to the confusion. Whv is the standardized death rate from cancer of tne lungs in Great Britain 3 times higher than that in tne United States - 231 in comparison to 723 (races per million)? It would indeed be very informative to have some answers to this list of unanswered questions before being able to form an opinion; and it might be that a few answers could influence or modify any conclusion concerning a causal relationship. PURPOSE OF THIS STUDY. The ppuurpose of this investigation is to try to learn aB precisely as possible the incidence of pulmonary cancer m the group of asbestos mining workers; to know the inciaence m groups of employees with severe or insignificant exposure and to know the incidence in groups with or without asbestotic fibrosis. The Saranac Laboratory and many other investigators were interested in a complete study which would include an epidemiological and an experimental investigation ano which would permit to'ascertain whether or not a relationship exists between the inhalation of asbestos dust and primary pulmonary cancer. This racer is a preliminary and incomplete report of the epidemiological investigation and the Saranac Laboratory, once the investigation has been achieved, will publish a final report. METHODS AND MATERIALS, This study was rendered possible mainly because there exists in Thetford Mines a co-operative industrial clinic where all the employees working in the different asbestos companies ` are required to have a pre-employment examination, plus an annual periodic examination completed each time by a standard stereogram. At this clinic it was easy to analyse all the medical records, the death certificates, the protocols and the pathological findings of the necropsies'and to review the series of chest roentgenograms of each employee. Thetford Mines being a small city of 13,000 it was also easy to contact and to discuss with the treating physician the nature of any respiratory episode, to have follow-up reports on any suspicious cases and to collect additional details on the cause of the deaths. In summary, this study is based on the results and findings obtained from the analysis of the medical files of 3,957 employees having worked in the asbestos industry from 2 - 6 0 years, on the findings from 53 necropsies, on the details collected from the death certificates, on the follow-up reports of cases sent to specialized centers for more complete investigation and d iagnos is * It is possible, and more than likely, that cases of pulmonary cancer have been missed; nevertheless, we think that we have employed a standferd procedure in this investigation and that the results therefore are of sufficient interest to make this Dublication worthwhile* RESULTS. Before submitting the results of this investigation, it would seem proper to give a few routine tables m oraer to reach a better understanding of this communication. TABLE 1 . POPULATION SAMPLED. Ape group distribution of 3,957 esoestos workers. Auij G n O u ? S Number of Employees 15 - 19 20 - 29 30 - 39 40 - 49 50 - 59 1 1 1 60 - 69 70 k Over t TOT 76 1113 1 0 9 1 766 505 307 99 35 This table gives the age group distribution of the sar; pled _ population ana needs no comment except to mention that the average age of the asbesios workers is somewhat higher than ohat of the average industrial worker; i.e., 35 in comparison to 33 for most other industrial groups. This remark is logical when we know that the labor turnover in the Quebec Asbestos Mining Industry is about the lowest of aul tne industries in the whole of Canada. This first table also shows that some 2,000 asbestos workers are 35 years of age and over - a repre sentative group for the study of a cancer problem. Years in the Industry TABLE 2 . Years employed in the asbestos industry by 3,957 asbestos workers.________ 2 - 4.S ..... .................. 5 - S.8- 10 - 14.9 15 - IS.9 20- 24.9 25- 34.9 35 L Over Number of Employees Man - Years 640 1520 1060 645 7420 7740 476 8092 281 6152 546 14742 309 : 1 12360 [ REMARKS: 2,257 men have spent 10 years and over in the asbestos industry. The second table indicates the number of years spent in the asbestos mining industry by the 3,957 employees studied . Of course this table is not as significant as one indicating ; the specific exposure for each employee by categories; but after many attempts it has seemed impossible to find a common denominator which would permit to add together the years spent in different . degrees of exposure by the same employee. The man-years exposure has in the mind of many invest!- . gators no great meaning in general, but in this case the fact that 56,456 man-years.asbestos exposure having given rise to only 10 confirmed cases of pulmonary cancer might indicate that we are not facing an acute problem. . i The following table 3 shows classification of various j- exposures in the asbestos mining industry. I realize that such l a classification could be discussed at length and possibly i xw a s u c s w b i i i u u s i r y | o s i n - , o s i cm w,..-_ otJier dusty industries, it is impossible to translate with a ^ strict mathematical precision the different concentrations of dust particular to each iob. This classification is given not withstanding its limitations because it is based on dust counts performed by different competent agencies and, moreover, because we feel that a satisfactory classification is very useful in under standing more clearly scientific and medico-legal problems, TABLE 3. ' Classification of various i exposure in the asbestos mining industry. iyos Estimated ree of azard. 0 1 2 3 5 Industrial Operations AT I."0SPPZHIC Total dust count L.P.P.C.F. of air sampled. COKPITIOKS rercent fiber count Open Pit, Shops Open Pit: Box Loader, Cobber Dump Primary Crusher Dryer Concentrating Underground: all jobs under wet condition Short exposure of skilled employees Open Pit: dry drilling Secondary Crushing Storage Bin Less than 1 1 - 3 1- 3 2- 3 2-6 2- 5 3- 6 '2 - 10 - 12 10 - 14 Less than 2 Less than Less than 2 5 . 6 : 5 1- 2 1- 2 4-6 4-6 Underground: cry drilling Grizzlies Shed Cobbing Shipping Shed; Cleaners, Pilers Hill: Lillwrights, Oilers, Sweepers Testers. Bagging Department 10 - 15 5-15 3-5 4-15 10-25 8 20 - 30 1-3 2 14 - 16 10 - 14 25 9 20 28 This table indicates that the total dust count and the percent fiber count are both constituents of the degree of hazard, meaning that a rather low total dust count may become a risk when the percentages of fibers is high and inversely, that a high total dust count may also become harmless in producing pulmonary fibrosis if the fiber percent count is low. The percentage of fibers in relation to the total count is calculated for fibers 5 microns and over, anc on the principle that only particules having a length at least twice its width are fibers. As you may see in the table, the industrial operations are grouped in 6 different categories and these categories are again sub-divided by a dduble line in two main groups. The upper group includes the jobs which in our experience do not produce fibrosis of some clinical importance and the lower group the jobs which can produce asbestosis. There is an obvious explanation why the men working in the open pit do not develop asbestosis and also why the men work ing as baggers might develop asbestosis, but it is more difficult to explain why some industrial operations with about the same dust concentration as-secondary crushing, storage bin on one part, the grizzlies and shed cobbing on the other part have been classified in different categories. We admit that in adopting such a ^ classification we have been influenced by our clinical findings to some extent, but also by the fact that in the operations of categoi 3, the fiber concentration is. more constant and work much heavier than in the operations of category 2. There is a marked different in "the degree of hazard of categories 1,2 and 4 and 5, but the difference is not so marked for the categories 2 and 3* This table is important in order to fully understand those to follow. It is true that the main purpose of this presentation is to report the incidence of pulmonary cancer in a group of 3,957 asbestos workers, but the nude statement that 10 cases of pulmonary cancer have been detected would not be significant unless we can compare this prevalence with that in comparable groups. : This task of finding a good comparable group or a control group in this study as in any similar studies is very 'difficult. We wish it had been possible to find a control group in other industries or in other industrial centers in the Province of Quebec or elsewhere in Canada. We soon realized that no other industries were interested in that problem of cancer of the lungs - nor did they have the necessary data for comparison. No other industrial city has ever had two-thirds of its male adult populatio of the same age group so closely medically supervised with a clinical and routine roentgenographic examination as has been done - in Thetfcrd Mines for the last 7 years. The mass surveys m different cities did not help the situation; the findings were too dificient doubtless because a too small proportion in the 40-year and over age group is taking advantage of the mass survey. ^ As a matter of fact, a mass survey in Thetford Mines m 1950 by the Provincial Department of Health did not detect a single case of pulmonary cancer as in most of the other centers, and the analyi of the results is not very helpful. It seems probable that the general increase in the frequency of lung cancer is not purely apparent, but when we observe m many cities a sudden and important increase in the lung cancer mortality rates such as the increase in the City of Montreal from 7.7 in 1946 to 12.9 in 1949, we must admit that the medical diagnosis facilities are responsible to an appreciable extent for such an increase. Therefore the exclusive analysis of death certificates in various centers which do not have the same medical facilities, has to be used with caution not should it be used unless the facilities are comparable. In this study the comparative statistical analysis of the death certificates was not used because in the opinion of the official < statistician of the City of Montreal and of the Statistician of the National Cancer Institute of Canada, the death certificates of the asbestos group condisted of a highly selective group and a similar selective group was not available elsewhere For all the reasons mentioned above and the fact of being unable to make a better selection, we decided to compare the incidence of pulmonary cancer in different groups of asbestos workers who have been submitted to the sane medical investigation, and who at the same time were presenting enough characteristics to permit certain conclusions or impressions Lumber of Pr.plcyees TABLE 4 . Incidence of pulmonary cancer according to degree and length of exposure by age groups. GROUP 1. Unsignificant exposure AGE GROUPS 16 - 39 40 - 86 GROUP 2. Significant exposure AGE GROUPS ' 16 - 39 40-86 - . 2229 ' 1367 56 305 Prevalence of Pulmonary 0 Cancer ( 6 (0.44a ) 0 4 (1.31/i) RELLARKS: Uniignificant exposure includes ir.en with exposure 0-1-2 and less than 15 years 3-4-5. Significant exposure includes only men with more than 15 years 3-4-5. (See Taole 3) The usual calculations of the standard error show that ' the observed difference in percentages of incidence in the 2 . groups (.67) is inferior to twice the Standard Error (1.346). This table shows that there is no statistical evidence | that the incidence of pulmonary cancer in the group 2 including ; the employees who have sustained severe exposure and all those who ; have also developed asbestos is, is higher than in group 1 of employees those without significant exposure and without any clinical asbestosis. It is recognized that this table might lose a large part of its meaning if it is bhown that any intensity of asbestos inhalation or any amount of asbestotic fibrosis could be considered as cancerigenic because then a large number of employees in group 1 will be transferred to group 2 and it is probable that an unknown number of pulmonary cancers in the group 1 would also have to be transported to group 2, changing raridly the observed difference in incidence as well the conclusione As a logical complement to this table, we wish we could give a long series of other tables showing the incidence of pulmonary cancer in groups with recent or remote exposure; in groups with gradual exposure of 1-2 to 15 years or a similar exposure of long duration, 15 years and over; also in groups with extensive exposure and asbestosis or without asbestosis^ The data obtained from such tables might tell us in the hypothesis of a causal relationship whether the inhalation of asbestos dust is more important than the presence of asbestosis itself also what approximative degree of asbestos inhalation can bp considered as predisposing to cancer0 Kunb er Autopsied 2'uTiber of Fv Ire nary Cancer Percent in Each Group TABLE 5 . Comparative Incidence of Pulmonary Cancer in 2 croups of 53 Autopsied asbestos workers. -- GROUP 1. 1------ -.... Employees with . Asbestosis GROUP 2. Employees without AsbestosiB TOTAL 34 19 53 4 g 10 11.7^ w1X1#zef This table shows the prevalence of pulmonary cancer :.n a series of 53 autopsied asbestos workers- having worked in the asbestos mining industry from 17 to 40 years in different degrees of exposure,, This series of autopsies is not as important as the series published in the Annual Report of Great Britain for the year 1947, but can be considered .as less selective and more representative in not being composed from cases of asbestosis exclusively but composed of all the employees wrho happen to be autopsied; although it should be mentioned that there was an -H- mvoluntary selection in the sense thet most of these employees have been autopsieb because they were presenting some respiratory symptoms . This coincidental selection might explain to some extent the high percentage of cases of asbestosis, but in many instances "the amount of asbestotic fibrosis detected was described as minimal and of no clinical importance because not sufficient to produce symptoms. Because the observed difference in percentages of incidence is inferior to twice the Standard Error, this table does not reveal a statistical evidence of a causal relationship between asbestosis and pulmonary cancer. Unless we have the opportunity to reifcrm an autopsy -n'i c-.ll employees who die, it remain aif fic ult tc expla in why in our series there are less cases ' pulno nary can cer in the asbestotic group and I think we here a good illust ration as to why many statisticians counse not to craw any cc nc'Lusions from statistics based on a selectiv group even if such a group be in the 'autopsy' category becaus the ro le pi aye d by the factor co-incidence might be too great. TABLE 6 Eeaths from Pulmonar}' Cancer as a proportion of deaths from Cancer of all sites. 1S40 - 150 Number of Cancer All forms Province of Quebec ity of Montreal uty of Quebec -ity of Thetford Mines 43643 15247 2543 172 Number of Pulmonary Cancer 1393 918 94 . 9 Percentages 3.2 6.0 3.7 5.2 Table 6 was prepared for the purpose of determining if the ratio between the number of cancer deaths all sites and the pulmonary cancer deaths was somewhat different in Thetford Mines from the ratio observed in few other control groups. First it should be mentioned that about 901o of the cases of pulmonary cancer in Montreal and 100yo of the cases of the Thetford Group are autopsy cases and both -cities have thoracic clinics, so these two groups are reasonably comparable. In Quebec City ' for the specific period 1945 - 1950 inclusive, 51 of all cancer deaths were also pulmonary cancer. It was thought that had a special factor existed in Thetford Mines the ratio between the number of total cancer and.the number of pulmonary cancer would have been differento The difference observed here is not sufficient to draw any conclusion either positively or negatively, TABLE 7 . Comparative 10 Years Expectancy and 10 years Prevalence of Pulmonary Cancer in 2 cities. j PLACE i i________ ___-___________ ! Thetford Mines 1 ' . 1 ' i Ecntre&l ! YEARS 1941 - 1850 1941 - 1950 10 YEARS EXPECTANCY 10.5 693 10 YEARS PREVALENCE 9 856 ; Based on U.S, Public Health Service Report 2557 A random population of 48,833 giving a year pulmonary cancer expect ancy of 7 cases per 100,000 population. Table 7 was prepared at the suggestion of Dr. Philipps, < Statistician for the National Cancer Institute of Canada who thinks that the comparative study of the 1C years expectancy and 10 years actual prevalence of pulmonary cancer in Thetford Mines and in Montreal will be more informative and more conclusive than analysis of the mortality rates. According to the surfey of Dr. Dorn, taking random population of 4$, $33, an annual inci dence of pulmonary cancer of 7 cases per 100,000 can be expected, giving a year expectancy of 7 It is true that Dr. Dorn's survey was made in 1943-45 and that the year expectancy might have increased recently As a matter of fact, Watson of Saskatoon, Canada, found in 194$ a year expectancy of $.5; therefore, a year expectancy of 7 is a rather conservative standard. On that basis Thetford Mines with an average population of 15,000 for 1940 - 1950 period, is supposed to have 10,5 casesi i t of pulmonary cancer, and the actual prevalence is 9 cases. Again it seems logical to think that the 10 year prevalence for pulmonary cancer in Thetford Mines where two-thirds of its adult population is working in the asbestos industry would be higher than the normal 10 year expectancy, should the factor asbestosis be considered carcinogenic SUMMARY. . The etiology and the pathogenicity of the pulmonary ' cancer in relation to asbestos factor is as obscure and confusing as those of cancer in general, and in presence of contradictory data, the many different aspects of the problem should be considre before arriving at a conclusion. ' The purpose of this study is to learn the incidence of pulmonary cancer1amongst the 3,957 asbestos mining workers and to compare this incidence with other comparable groups. This in- . complete epidemiological report is a contribution to a more complete investigation under progress at the Saranac Laboratory. . According to the standard procedure the medical files, the results of medical supervision, the annual stereograms of all the asbestos workers having worked from 2 to 60 years and the ; findings of 53 autopsies have been used as material ' The results have been tabulated and compared to control ; groups and we think that the data collected in the Asbestos Mining Industry are not exactly superposable to the results found in the English Asbestos Textile Industry of Great Britain and if they do not permit to deny a causal relationship between the inhalation of asbestos dust and the occurence of pulmonary cancer, they do not seem either to bring any positive evidence. discussion Si. KHOiSS, I vas interested in tr. Cartier's remark that the .uass survey -Pioyed in hi. group did not reveal ar.y patients rite early o r n e r y cancer. I presume that tee .pass survey vas not sufficiently large ar.d therefore this method of revealing a disease teicu is treatable and ofte:. curaiue ray not ainve been adequate. ' " In regard to tee 53 autopsied individuals, of ,,nos, 10 had pul .onary cancer r presute tney were autopsied because it -..as thought t..at they ray nave had pulmonary cer.cer. Those uere not routine .-.tousles? n"JT--D*TJ----TTw. '***0 * 1.-. yJiOahS: The duplication is clear teat teere is no drjrger fmr, oulnonam cancer to vomers iu-teis particular group. Perhaps teat inference is true. appears to ne that asbestosis is a very healthy ail_~--t -s concerned. iar as cance] hh.h Dnl.'li IED SPEAKER: nocsrre to asbestos? ur. Cariter, vuft are tns first signs of trouble iron ( DR. CldTIlP.: I dc not believe there are any specific.symptoms. If the fibro sis is extensive enougn t-iCre is dyspnea ana cyanosis, sometimes to an extreme degree. In our group ve have nad 9S coses of asbestosis. These iudivicuals have had a marled exposure to asbestos for years and many of them, cn reaching age 50 to 55, are mere dyspneic and seen to die mere rapidly without much disease. They go downhill rapidly,- vita in a few months. ml. Rr.0.r.TS: Cf what do they die? , DR. CARTIER: Some from cardiac disease and fr:n miscellaneous generalized diseases, some from bronchiectasis. In my experience there is no special pict except that they fail rapidly - in two cr three mentns. D?.. VGF.VALD: Ve nave been encouraging Dr. Cartier to continue tils study- of the rather isolated population of Thetford, and we are conducting a similar epic'emiological survey of a neighboring community which is also engaged in the mining and processing of asbestos. Ve suggested to Lr. Cartier tuat ne mi gut the incidence cf cancer in hiz exposed group in Thetier: review ing the cnest roentgenograms cf nis cases - the roentgenograms tavern during tee past If years, Admittedly, cases of pulmonary cancer 1111 be missed by that netned. Ve have considered sputum examinations but a.z ^resent the best ve can cc is t: study tne c^est roentgenograms of tuis large series cf incivi- duals exposed in a special industry. 1.*1 S: Did ye discover any cancer cases, in so doing? DR. CAETIrR: Yes, with the X-ray. Vo cases were revealed by tne mass survey all the cases were detected in the clinic