Ranking animal carcinogens: a proposed regulatory approach.

The nature and extent of positive evidence associated with animal carcinogens vary widely, yet present regulatory policy does not permit adequate discrimination among the many carcinogenic substances. Most are treated as if they pose equal potential risk to humans, and this is not consistent with the available data. Without knowledge of carcinogenic mechanisms, the evaluation of responses in intact mammalian surrogates best reflects the potential levels of human risk. An example of a scoring system is proposed by which animal carcinogens are ranked according to the most relevant toxicological evidence derived from animal and genotoxicity studies. Different classes of animal carcinogens could thus be recognized and would permit several regulatory options and provide a means to establish priorities for public and scientific concerns.