The genesis of cancer with chemicals.

In studying the sequence of events during the induction of cancer with chemicals, major emphasis in recent years has been given to the identification of possible carcinogens and to their metabolism and interactions with cellular constituents, such as DNA, in target cells. The repair of relevant chemical lesions seems to be important, and special emphasis can be given to the cellular aspects of chemical carcinogenesis, the biological nature of the initiated cells, and the basis for their growth into focal proliferations during promotion. A new model for the sequential analysis of steps during the earlier periods in cancer development in the liver with chemicals has been developed, delineating the probable role of cell injury as a rate-limiting step in cancer development in organs that are quiescent with respect to cell proliferation, and the possible beneficial role of the early events in chemical carcinogenesis in natural selection.