Race-Strain Factor Related to Hydrocarbon-Induced Mammary Cancer in Rats2

Abstract

A single dose of 7,12-dimethylbenz[a]-anthracene induced multiple cancers of the mammary gland rapidly in all Sprague-Dawley female rats, whereas under identical conditions rats of the Long-Evans strain had a low incidence of mammary cancer, with long induction time, a few tumors, and occasional regression of the cancers. The results were not significantly modified hy newborn rats of one strain foster-nursed by mothers of the other strain. The difference in susceptibility of these strains to hydrocarbon-induced mammary cancer is due to an inherited variation in their endocrine constitution with varying sensitivity of the mammary gland to the carcinogenic effect of the hydrocarbon. After multiple intravenous injections of the hydrocarbon, 94 percent of Long-Evans rats developed mammary cancer. The importance of inherited strain difference was nullified by multiple strong carcinogenic stimulation.