Estrogen receptors in androgen-induced breast tumor regression

The hormone-dependent 7,12-dimethylbenz(a)anthracene rat mammary tumor has been shown to regress when administered pharmacological doses of testosterone propionate. Tumor regression was correlated with estrogen receptor before and 15 to 20 days following testosterone therapy. A dramatic decline of receptor occurred in all regressing tumors, whereas those administered sesame oil alone maintained both growth and receptor content. Although receptor in regressing tumor was significantly less than in the untreated biopsies, the small amount of remaining receptor maintained the same binding affinity to estradiol, showing that testosterone affects the number and not estrogen affinity of the estrogen receptor. These studies suggest that testosterone depletion of estrogen receptor may be causally related to tumor regression.