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Observations on the Hormone Sensitivity of 7,12-Dimethylbenz()anthracene-induced Mammary Tumors in the Sprague-Dawley Rat¹

Kettering-Meyer Laboratory, Southern Research Institute,² Birmingham, Alabama 35205

Mammary tumors induced by a single feeding of 7,12-dimethylbenz()anthracene to female Sprague-Dawley rats were used to determine (a) the relationship of hormone responsiveness to tumor mass or to time from carcinogen exposure to treatment and (b) the influence of exogenous steroids on ovariectomy-induced tumor regression. The results of these studies suggest a gradual decline in response to ovariectomy or treatment with 2--methyldihydrotestosterone propionate as the time from carcinogen exposure to initiation of treatment or surgery increased. Androgen treatment of rats that were 180 to 210 days beyond carcinogen exposure caused significantly less regression of large tumors than of small tumors. When tumor-bearing rats were ovariectomized and immediately treated with testosterone propionate, 2--methyldihydrotestosterone propionate, or diethyl stilbestrol, tumor regression was significantly lessened as compared to ovariectomy controls. Testololactone, 1-dehydro did not exhibit this effect. Delayed treatment with the former three agents following ovariectomy-induced tumor regression resulted in tumor growth stimulation to various degrees during the period of treatment. Neither the temporary inhibition of regression nor the temporary stimulation of tumor growth significantly altered the total period of remission.

¹ This investigation was supported by the Endocrine Evaluation Branch, General Laboratories and Clinics, National Cancer Institute, USPHS, under Contract PH 43-66-71.

² Affiliated with Sloan-Kettering Institute for Cancer Research, New York, N. Y.

Received 6/16/69. Accepted 10/ 9/69.