Estrogen induced growth of human breast cancer cells (MCF-7) in athymic nude mice is enhanced by secretions from a transplantable pituitary tumor.

MCF-7, a human breast carcinoma cell line, was maintained s.c. in female athymic nude mice for a period of 5-6 weeks. Administration of estrogen (s.c. pellet of 17 beta-estradiol and estrone in drinking water, 0.5 mg/l) to these mice resulted in sustained (P less than 0.001) growth of MCF-7 tumors. Grafting of a prolactin and growth hormone secreting rat pituitary tumor to the estrogen-treated mice resulted in an increased (P less than 0.05) rate of MCF-7 tumor growth. MCF-7 did not grow in athymic nude mice grafted with rat pituitary tumor alone or in mice without hormone treatment (controls). Thus, secretions of pituitary hormones alone are not capable of promoting in vivo growth of MCF-7 although such secretions significantly enhance estrogen-induced growth of this cell line. A synergism between pituitary hormones and estrogen for in vivo growth of a human breast carcinoma has been demonstrated in this study.