Mammary neoplasia in beagles exposed to gamma radiation during development

A total of 261 Segment III female beagles had developed one or more mammary neoplasms as of December 31, 1978, and 192 (74 percent) of these had been irradiated. Sixty-nine of 180 controls (38.3 percent) had tumors. The incidence in the various irradiated groups ranged from a low of 16 of 120 (13.3 percent) in dogs exposed to 100R at 70 days postpartum (dpp) to a high of 48 of 120 (40 percent) in dogs exposed to 100R at 365 dpp. No significant differences were found among the different experimental groups with respect to the crude incidence of benign or malignant neoplasms or both combined. Since the colony is relatively young with respect to mammary neoplasia, this subject bears continued consideration