Multiple factors in carcinogenesis.

Before making some comments on multiple factors, I would like briefly to refer to the discussion at this conference. There has been no reference, strangely enough, to a law known as the Delaney Amendment. Asbestos is a carcinogen. It is apparently being deliberately added to certain drugs and foodstuffs by particular processing and manufacturing practices. Surely, when asbestos is introduced into foodstuffs by deliberate processing this is a clear cut contravention of the Delaney Amendment. The whole question of the relevance of the Delaney Amendment to asbestos in water is a complex legal matter. Suffice it to say that I think it is possible to develop a substantive legal argument that the deliberate discharge of carcinogens such as asbestos into water represents a contravention of the Delaney Amendment. Now with relation to multiple factors this is a fascinating area in which epidemiology has blazed the trail and toxicology has lagged sadly behind. I think that with the little we have heard here on the role of smoking and asbestos, and from the literature on the subject, it becomes clear that smoking does enhance the incidence of bronchogenic cancer following occupational exposure to asbestos. Similar considerations relate to uranium although, however, the question of the synergistic or other positive interactions between smoking and radon daughters appears somewhat compounded by the fact that silica dust may also be involved, and thus we appear to have possibly three factors: smoking, silica dust, and radon daughters. Now while it is true that