AVOIDED AND AVOIDABLE RISKS OF CANCER

Despite the considerable efforts and funds devoted to cancer research over several decades, cancer still remains a mainly lethal disease, Ca ncer incidence and mortality have not declined at the same rate as oth er major causes of death, indicating that primary prevention remains a most valuable approach to decrease mortality, There is general agreem ent that environmental exposures are variously involved in the causati on of the majority of cancer cases and that at least half of all cance rs could be avoided by applying existing etiologic knowledge. There is disagreement, however, regarding the proportion of cancer risks. attr ibutable to specific etiological factors, including diet, occupation a nd pollution, Estimates of attributable risks are largely based today on unverified assumptions and the calculation of attributable risks in volves taking very unequal evidence of various types of factors and tr eating them equally, Effective primary prevention resulting in a reduc tion of cancer risk can be obtained by: (i) a reduction in the number of carcinogens to which humans are exposed; or (ii) a reduction of the exposure levels to carcinogens, Exposure levels that could be seen as sufficiently low when based on single agents, may actually not be saf e in the context of the many other concomitant carcinogenic and mutage nic exposures, The list of human carcinogens and of their target organ s might be quite different if: (i) epidemiological data were available for a larger proportion of human exposures for which there is experim ental evidence of carcinogenicity; (ii) more attention was paid to epi demiological evidence that is suggestive of an exposure-cancer associa tion, but is less than sufficient, particularly in identifying target organs; and (iii) experimental evidence of carcinogenicity, supported by mechanistic considerations, were more fully accepted as predictions of human risk.