Physical activity and cancer prevention: animal-tumor models.

PURPOSE: The aims of this paper are to briefly review the types of animal and tumor models used in carcinogenesis studies and to consider their utility in studies of physical activity and cancer.
METHODS: Published data from animal studies using tumor models for which corresponding human epidemiologic evidence shows a clear association between physical activity and that cancer (i.e., colon and breast) are reviewed.
RESULTS: A variety of animal-tumor models have been used in cancer studies including spontaneous tumors, chemically induced tumors, orthotopic and syngeneic tumor transplantation, injected tumors, and genetically engineered (transgenic, knockout, and mutation-induced) mice with a predisposition to neoplasia. The most commonly used animal-tumor model in the study of physical activity has been the chemical carcinogenesis model. Methodological limitations of the various animal-tumor models are described including variations in dosing, route of administration, and type of carcinogen used, and forced versus voluntary exercise effects.
CONCLUSIONS: Animal-tumor models are useful for understanding specific aspects of the carcinogenesis process and the interaction of this process with exercise. There is no one animal-tumor model that is ideally suited for studying physical activity interventions. However, animal-tumor models can be viewed as complementary to epidemiologic studies and human clinical trials in the area of physical activity and cancer prevention.