A New Way to Look at Old Questions of Silica Carcinogenicity

Although results from some epidemiologic studies indicate an association between silicosis and lung cancer, other investigations have not confirmed these findings. The discrepancies may be related to methodologic problems. These include the lack of autopsy confirmation for the presence of silicosis or of information on the histologic lung cancer type, and unavailable or uncertain estimates of exposures to silica and to known carcinogens that may interact with silica or silicosis. This study will be designed to avoid the above weaknesses and reconcile observations in humans with results from animal studies, which show a carcinogenic effect for silica. We have formulated a series of testable hypotheses based on plausible mechanisms of carcinogenesis. These hypotheses suggest that silica interacts with known carcinogens (e.g., radon or cigarette smoke), and that only specific types of lung cancer are associated with silica or silicosis: (1) if silica or silicosis of lung parenchyma causes proliferat...