Species differences in carcinogenesis.

There are differences in response of different species to many carcinogens. Different organs respond to particular carcinogens, there are differences in potency (including resistance of some species), and there are varying effects of other parameters. Although animal studies identify carcinogens, it is impossible to predict accurately the potency or the target organ in humans of any carcinogen. Inter-species differences in response to carcinogens can be due to differences in metabolism and activation. However, even in the case of directly acting carcinogens, such as alkylnitrosoureas, quantitative differences in alkylation of DNA are insufficient to explain the differences in response of particular organs. Yet unknown reactions or interactions of carcinogens must be key factors in inter-species differences.