Mechanisms of Chemical Carcinogenesis: Theoretical and Experimental Bases

Abstract

Although ionizing radiation, infectious biological agents, and genetic determinants play significant roles in the causation of human cancer, environ-mental chemical agents and mixtures of such agents, both exogenous and endogenous to the living organism, are causally involved, too (Doll and Peto 1981; Wynder and Gori 1977). While lifestyle factors such as diet, sexual mores, and reproductive history may not be considered under the heading of chemical carcinogenesis in the usual sense, in all of these (just as in cigarette smoke) chemicals and mixtures of chemicals are the predominant components that cause human cancer. A potential exception in this group are those neoplasms developing as a result of sexual promiscuity, where the human papillomavirus may play a major role in genital cancers, both male and female (Zur Hausen 1987). Until the past decade, the chemical induction of cancer was the principal experimental tool of carcinogenesis. Within the past 10 years experimental investigations of viral carcinogenesis have equalled or exceeded those in the chemical induction of cancer. However, our understanding of the mechanisms of the chemical induction of neoplasia preceded our understanding of such mechanisms in the viral induction of cancer (Miller 1978).