CRITICAL SIGNIFICANCE OF BREAST STRUCTURE IN THE INDUCTION OF MAMMARY CANCER IN THE RAT

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Abstract
The physiologic state of the mammary tree, dependent on endocrine effects, is of critical importance in rats fed 3-methylcholanthrene (3MC). Every normal female control rat developed mammary cancer before 92 days. Cancer of the breast did not form in the atrophic mammary glands of hypophysectomized rats. The incidence of breast cancer was significantly reduced in rats with profound mammary hyperplasia, of gestational or lactational type, induced in several ways; a highly effective blocking procedure was the administration of amounts of equine gonadotrophin sufficient to produce intense and long continuing stimulation of the ovaries and of the mammary gland with persistent lactation. 9-[alpha]-Bromo-11-ketoprogesterone (BKP) is the most effective agent as yet discovered in accelerating the development of mammary carcinoma in intact rats fed 3-MC. This BKP-induced acceleration of cancer development was abolished by the concurrent administration of estradiol-17beta; the incidence of mammary cancer was significantly reduced or the appearance of tumors was delayed while at the same time the gestational effects of BKP were profoundly enhanced by the phenolic estrogens.