Crystalline Silica and Lung Cancer: The Problem of Conflicting Evidence

Abstract

The IARC Working Group, in 1997, had considerable diffi culty in reaching a decision and might well not have done so had it not been made clear that it was concerned with hazard identification, not risk. Other authors have explained the complexity of the mechanistic findings; we do so with the epidemiological. Of the many studies reviewed by the Working Group, excluding those of registered silicotics, nine were identified as providing the least confounded evidence. Four studies which we con sidered positive included two of refractory brick workers, one in the diatomite industry and our own in pottery workers; the five which seemed negative or equivocal included studies of South Dakota gold miners, Danish stone workers, US stone workers and US granite work ers. This further example that the truth is seldom pure and never simple underlines the difficulty of establishing a rational control policy for some carcinogenic materi als.