Biochemical events in nitrosamine-induced hepatocarcinogenesis: relevance of animal data to human carcinogenesis.

Administration of carcinogens to experimental animals results in the early formation of phenotypically altered cell foci. Evidence suggesting their intermediary role in hepatocarcinogenesis, and some of their biological properties are reviewed. Two concepts relating to the mechanism of tumour promotion are described briefly, i.e., the 'resistant cell' hypothesis and that of 'overexpression of adaptive growth'. It is concluded that studies on liver foci may be helpful in elucidating the nature of the events involved in the initiation of carcinogenesis. Some aspects relating to human hepatocarcinogenesis are also considered briefly.