Abstract
The valid extrapolation of carcinogenesis data from one species to another depends, in part, on strong similarities of the metabolic and cellular mechanisms involved in the carcinogenic process and similarities in the nature and behavior of the various lesions that appear during the development of neoplasia between the species involved. Although there are many biological differences between the various rodent species used in carcinogenesis research, there are more similarities, in keeping with the surprising unity of basic cellular and tissue organization and function that is evident throughout biological systems at every level of evolutionary development. An understanding of intraspecies similarities and differences, especially as these modify the morphologic responses of the host to carcinogenic chemicals, is of central importance if carcinogenesis data from one species are to be used to predict carcinogenic risk in another. In this manuscript the histopathology of the various lesions that appear during chemically induced cancer of the liver, pancreas, and bladder in several rodent species has been selected to compare and contrast similarities and differences that exist among them and among the spontaneous premalignant lesions and carcinomas of these organs in humans.