The relationship between crystalline silica and lung cancer has been the subject of many recent publications, conferences, and regulatory considerations. An influential, international body has determined that there was sufficient evidence to conclude that quartz and cristobalite are carcinogenic in humans. The present authors believe that the results of these studies are inconsistent and, when positive, only weakly positive. Other, methodologically strong, negative studies have not been considered, and several studies viewed as providing evidence supporting the carcinogenicity of silica have significant methodological weaknesses. Silica is not directly genotoxic and is a pulmonary carcinogen only in the rat, a species that seems to be inappropriate for assessing particulate carcinogenesis in humans. Data on humans demonstrate a lack of association between lung cancer and exposure to crystalline silica. Exposure–response relationships have generally not been found. Studies in which silicotic patients were not identified from compensation registries and in which enumeration was complete did not support a causal association between silicosis and lung cancer, which further argues against the carcinogenicity of crystalline silica.
From the University of Alberta, Alberta, Canada (Dr Hessel); Exxon Biomedical Sciences Inc, East Millstone, N.J. (Dr Gamble); Yale University School of Medicine, New Haven, Conn. (Dr Gee); Safety Health Environment International Consultants, Spruce Grove, Alberta, Canada (Dr Gibbs); the Department of Pathology, University of Calgary, Health Sciences Centre, Calgary, Alberta, Canada (Dr Green); University Campus, London Health Sciences Centre, London, Ontario, Canada (Dr Morgan); and the Department of Pathology, University of Vermont College of Medicine, Burlington, Vermont (Dr Mossman).
Address correspondence to: Patrick A. Hessel, PhD, 13–103 Clinical Sciences Building, University of Alberta, Edmonton, Alberta, Canada T6G 2G3; e-mail email@example.com.