Silica, silicosis, and lung cancer: A response to a recent working group report

The relationship between crystalline silica and lung cancer has been the su bject of many recent publications, conferences, and regulatory consideratio ns. An influential, international body has determined that there was suffic ient evidence to conclude that quartz and cristobalite are carcinogenic in humans. The present authors believe that the results of these studies are i nconsistent and, when positive, only weakly positive. Other, methodological ly strong, negative studies have not been considered, and several studies v iewed as providing evidence supporting the carcinogenicity of silica have s ignificant methodological weakness. Silica is not directly genotoxic and is a pulmonary carcinogen only in the rat, a species that seems to be inappro priate for assessing particulate carcinogenesis in humans. Data on humans d emonstrate a lack of association between lung cancer and exposure to crysta lline silica. Exposure-response relationships have generally not been found , Studies in which silicotic patients have not identified from compensation registries and in which enumeration wets complete did not support a causal association between silicosis and lung cancer, which further argues agains t the carcinogenicity of crystalline silica.