Initiation and promotion in hepatocarcinogenesis.

Initiation and promotion have been recognized as essential parts of the multi-stage concept of chemical carcinogenesis. In the liver, initiation by genotoxic carcinogens results in appearance of foci of phenotypically altered hepatocytes. Accelerated growth and phenotypic changes of these foci during tumor promotion by phenobarbital are described, and possible mechanisms of initiation and promotion considered.