Mammary carcinogenesis-enhancing effect of adrenalectomy in irradiated rats with pituitary tumor MtT-F4.

Mammary carcinomas were found at autopsy 98--100 days after irradiation in 12 of 14 (86%) multiparous Fischer female rats which had been adrenalectomized and given grafts of secretory pituitary tumor strain MtT-F4 soon after exposure to gamma-rays or fission neutrons. A single carcinoma was found in 1 of 10 unirradiated, MtT-bearing, adrenalectomized animals. When adrenalectomy was not done, no tumors were found in 8 unirradiated or in 13 irradiated MtT-bearing rats rats. In view of the well-established finding that Cortisol is essential for milk production, we suggested as a working hypothesis that, in the presence of high titers of mammotropic hormone and adrenal corticoids, differentiation of a given cell for milk secretion reduced that cell's proliferative potential. When such differentiation was precluded by adrenocorticoid deficiency, more irradiation-altered mammary epithelial cells retained their high proliferative potential and contributed to carcinoma formation.