Evidence that the effectiveness of antioxidants as inhibitors of 7,12-dimethylbenz(a) anthracene-induced mammary tumors is a function of dietary fat composition.

A study of tumor incidence and tumor growth rates in 7,12-dimethylbenz(a)anthracene-treated female Sprague-Dawley rats fed different types and amounts of dietary fat indicates that the difference in tumor incidence may be a reflection of marked differences in the growth of neoplastic clones to a palpable size within the time frame of the study. In addition, the observation is made that some antioxidants which inhibit tumor development in animals fed commercial rations are not effective when given in purified diets.