ABSTRACT
Bioassays using rodent liver foci are widely used for the rapid detection of carcinogenic activity of chemicals. The detection of foci of altered hepatocytes after exposure to a test agent for a limited time, e.g., several weeks, or in stop-experiments including a recovery period was proposed nearly 40 years ago and has frequently been used for the quantification of the dose dependence of carcinogenic effects. The quantification of hepatocellular altered foci instead of fully developed hepatocellular tumors allows both a more rapid and more sensitive detection of hepatocarcinogenic effects. The interpretation of the studies must always take into consideration “spontaneous” or cryptogenic carcinogenesis in the rat liver. In contrast to the test for initiating activity, the selection of the appropriate marker reaction for the detection of the induced foci of altered hepatocytes may be crucial for the test for promoting activity, because the phenotype of preneoplastic foci may be modulated by the treatment of the animals.
