Effects of endocrinologic conditions associated with acute versus chronic lactation on the incidence of mammary carcinomas in irradiated rats: brief communication.

Groups of female Fischer rats received 500 rads of gamma-irradiation and were maintained in hormone states that promoted or inhibited lactation. Chronically lactating rats developed no mammary tumors. Rats did not lactate or lactated acutely during the period surrounding irradiation developed similar numbers of carcinomas.