Environmental Health Perspectives 105, Supplement 5, September 1997: Article by Case and Dufresne

Environmental Health Perspectives 105, Supplement 5, September 1997

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Asbestos, Asbestosis, and Lung Cancer: Observations in Quebec Chrysotile Workers

Bruce W. Case ^1,2 and André Dufresne ²

¹ Department of Pathology, ² Department of Epidemiology, Biostatistics, and Occupational Health, McGill University, Montreal, Canada

Abstract
One prospective epidemiologic study of asbestos cement workers with radiological small opacities has been cited as a rationale for attributing excess lung cancer to asbestosis. This approach could have considerable practical value for disease attribution in an era of decreasing exposure. However, a recent International Agency for Research on Cancer review concludes that the mechanisms of production of asbestos-related lung cancer are unknown. Asbestosis, therefore, cannot be a biologically effective dose marker of lung cancer susceptibility. Asbestosis nonetheless would be useful in identifying asbestos-attributable lung cancer cases if it could be proven an infallible exposure indicator. In this study, we tested this hypothesis in the chrysotile miners and millers of Quebec, Canada. We examined exposure histories, autopsy records, and lung fiber content for 111 Quebec chrysotile miners and millers. If the hypothesis of an asbestosis requirement for lung cancer attribution were accurate, we would expect an asbestosis diagnosis to separate those with lung cancer and high levels of exposure from those with lower levels of exposure in a specific and sensitive manner. This is the first such study in which historical job-based individual estimates based on environmental measurements, lung fiber content, exposure timing, and complete pathology records including autopsies were available for review. We found significant excesses of lung tremolite and chrysotile and estimated cumulative exposure in those with lung cancer and asbestosis compared to those with lung cancer without asbestosis. However, when the latter were directly compared on a case-by-case basis, there was a marked overlap between lung cancer cases with and without asbestosis regardless of the measure of exposure. Smoking habits did not differ between lung cancer cases with and without asbestosis. In regression models, smoking pack-years discriminated between those with and without lung cancer, regardless of asbestosis status. Most seriously, the pathologic diagnosis of asbestosis itself seemed arbitrary in many cases. We conclude that although the presence of pathologically diagnosed asbestosis is a useful marker of exposure, the absence of this disease must be regarded as one of many factors in determining individual exposure status and disease causation. -- Environ Health Perspect 105(Suppl 5):1113-1119 (1997)

Key words : asbestos, asbestosis, lung cancer, compensation, causation, lung burden, disease mechanisms, exposure assessment, risk assessment, attributable risk

This paper is based on a presentation at The Sixth International Meeting on the Toxicology of Natural and Man-Made Fibrous and Non-Fibrous Particles held 15-18 September 1996 in Lake Placid, New York. Manuscript received at EHP 26 March 1997; accepted 6 June 1997.
Address correspondence to Dr. B. Case, McGill University, 3375 University Street, Montreal, Canada H3A 2B4. Telephone: (514) 398-7192, ext 7466. Fax: (514) 931-6417. E-mail: case@pathology.lan.mcgill.ca
Abbreviations used: IARC, International Agency for Research on Cancer; MPCFY, million particles foot ³ years.

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Last Update: October 28, 1997