Occurrence and Transplantation of Carcino- gen-Induced Hyperplastic Nodules in Fischer Rats 1,2

15, or 20 mg 7,12-dimethylbenzlalanthracene (DMBA) in sesame oil in a single dose by gastric intubation. Mammary gland tumors or hyperplastic nodules, or both, were found in all treated animals, whereas none was observed in the sesame oil-treated controls. Nodules appeared with about equal frequency in all dose groups. However, the number of lesions in all groups increased with time after carcinogen administration. Similar lesions were seen in the mammary glands of old male and multiparous female rats. The hyperplastic structures observed in the mammary glands of DMBA-treated female rats were placed into four categories by mor-phologic criteria derived from stained wholemounts and histologic sections: hyperplastic alveolar nodules, distended alveolar nodules, fibrous nodules, and ductal hyperplasias. Eighty hyperplastic alveolar nodules were seen in the mammary glands of anesthetized animals by intraductal injection of the animal's blood. These nodules were transplanted into the abdominal gland-free mammary fat pads of 3-week-old female rats. No tumors de