Document wgKj1BxELVzaVKbZ9VYvd48q6

A. M. A. ARCHIVES OF ISOUSTRIAL HEALTH tnd exposure 10 asbestos hat been evident was not possible to trace 133 of these for since the report in 1913 by Lynch and Smith the whole period, but 5771 of the remaining of a cate in which lung cancer and ssbes- $958 were found to be stilt living in 1955 totit were both present. At additional cases or later. Of the 187 known dead, canter in which the two diseases coexisted were of the lung was considered to have been reported, a causal association appears to rosonab/y proved in 9 and to be strongly hasx been gradually accepted by many suggested in 3. authors, although some workers considered The members of the cohort were studied the correlation to be inconclusive. The pres* with respect to age, length of employment, ent study was undertaken in an effort to de a weighted average of their exposure, and termine whether a causal relationship did, their smoking habits. It was found that in fact, exist between exposure to asbestos, 4673 were smokers within the definition of and cancer of the lung. that term as used in this study. Thirty-four Since most earlier studies had been per cent of the cohort were more than 45 limited to enumerating the hutg cancers years of age. and thirty per cent had been found in certain selected samples, such as employed for longer than 20 years. Thirty cases coming to autopsy or death certificates per cent had a weighted exposure which in which asbestosis was mentioned, it was .placed them in the category ol highest ex apparent that they could not fulfill the re* posure. quirements of an epidemiological and sta tistical approach to the problem. The present study was. therefore, designed to meet the requirements of this method. Alter a preliminary survey to explore the availability of reliable 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 The mortality rate lor lung cancer, as computed on the basis ol nine "proved" deaths among the cohort was 25J per 100.000. When the three "suspected" cases were added, the "total" rate for the cohort rose to 33.8. The importance ol the suspected but unproved cases in determining, these rates has been reiterated because it is likely that such cases would not be included in the statistics for the general population and of exposure and who were in the industry because they influence the results so mark in 1950. Data relative to their characteristics edly. were collected and their status at the end of a six vear period of observation was determined. In the case of those who had . died, an exhaustire search of death certif icates and insurance records was carried out in order to determine as nearly as possible According to the findings in this study, the mortality rate from lung cancer docs not appear to increase with length of exposure or with degree of exposure, a fan which presents strong evidence against the carcinogenicity of asbestos. the exact cause ol 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, Comparison of the experience among the asbestos miners with that of various seg ments of the onexposed, comparable popu lation allows that the observed number of as well u the United States were calculated deaths among the miners is not significantly from statistics collected in the appropriate greater than the expected number. The rate places. Comparisons of the rates obtained for proved cases among the asbestos miners for asbestos workers and for the other popu (25.3 per 100,000) compares well with the lation groups were nude according to ac rate of 2ZS per 100.000 for the vest of the cepted statistical methods. Province, --i 2C 100X100 for adult Records were obtained on 6091 persons males throughout the Dominion of Canada. who fulfilled the criteria of the cohort. It It also compares satisfactorily with rater 650 Vo! IT. !w*. M*