Further investigations on induction of mammary cancer in mice by isografts of hypophyseal tissue.

Hypophyseal isografts to sites remote from the hypothalamus in otherwise untreated female mice produce prolactin continuously. The excessive stimulation of the mam mary glands by prolactin and progesterone in the graft-bearing animals may lead to mammary tumor formation. The effect of isotransplantation of a single hypophysis at various sites (subcuta neous, intraperitoneal, spleen, ovary, kidney) in MTA-free ( 9 O2oX cf IF)Fi female mice was investigated. Mammary tumor incidences of up to 80 per cent were observed in the experimental groups, as against a value of 2 per cent in the controls. Grafts of hypophyses of adult donors into the kidney were more effective than grafts into the spleen. Hypophyseal grafts of adult male donors were more effective than those of adult female donors. This sex difference was absent in the very potent grafts of infan tile donors. Even grafts of a hypophysis of very old donors produced prolactin con tinuously and induced mammary tumors in the hosts. Subcutaneous isografts of a single hypophysis frequently failed to "take," but mul