Inhibited growth in vivo of a mouse pregnancy-dependent mammary tumor (TPDMT-4) by an antiestrogen, 2alpha, 3alpha-epithio-5alpha-androstan-17beta-ol (10275-S).

TPDMT-4 mammary tumors, characterized by growth during pregnancy and postpartum regression, grew continuously in DDD virgin mice carrying pituitary isografts or 17 beta-estradiol plus progesterone pellets. In the experimental models, effects of 2alpha,3alpha-epithio-5alpha-androstan-17beta-ol(10275-S), testosterone, and ovariectomy were investigated. When tumors implanted with pituitary isografts into the fat pad reached palpable volumes, animals were ovariectomized or received 5 s.c. injections of 100 mug to 1 mg 10275-S or 300 mug testosterone weekly. Tumors regressed immediately after ovariectomy or after the start of 10275-S treatment and after approximately the 10th day of testosterone treatment. Cystadenomatous morphology with strong secretory activity was noticed in treated animals. Tumor growth induced by 17beta-estradiol plus progesterone pellets was inhibited completely or partially by 3 s.c. injections of 50 to 500 mug 10275-S or 100 mug testosterone weekly starting from the day after tumor and 17beta-estradiol plus progesterone pellet implantation.