Mammary tumorigenesis and chemoprevention studies in carcinogen-treated rats

The objectives of this review are to describe the induction of mammary gland tumors by chemical carcinogens and to discuss their application to mammary cancer chemoprevention research. Special emphasis will be placed on the dimethylbenz[a]anthracene (DMBA) and methylnitrosourea (MNU) models because of the extensive information available about the pathogenesis of tumor growth associated with these two compounds. Both models have been widely used in the investigation of novel cancer chemopreventive agents. The current status of a number of different approaches will be summarized briefly here to provide an overview of research opportunities. Despite the popularity of the DMBA and MNU models in laboratory studies of mammary cancer biology and prevention, neither of these carcinogens has ever been implicated in the etiology of human breast cancer. This shortcoming has prompted a growing interest in other relevant environmental chemicals which are capable of producing mammary tumors in experimental animals. The new models have yet to be fully characterized, but they may be more appropriate than the DMBA and MNU models as paradigms for assessing cancer risk in humans and for developing suitable cancer prevention strategies.