Abstract

Forty eight female Sprague-Dawley rats received a subcutaneous implant containing 12.5 mg estradiol ant the age of 3 weeks. Three rats were killed in 1, 2, 3, 4, 6 weeks and in every month during 2~12 months after implantation, and the breasts were examined by light microscope. In all rats, enlargement of terminal end buds was obseved in 1~2 weeks, maximum development of hyperplastic alveolar nodules in 3 weeks, and marked dilatation and secretion of alveoli or ducts in 1~12 months after implantation. Ductal epithelial hyperplasia was observed in 27 rats and carcinomas developed in 23 rats in 2~12 months after implantation. It was thought that the changes induced by estradiol are more similar to the human breast lesions, compared with changes induced by chemical carcinogens such as dimethylbenzanthracene(DMBA), because breast carcinomas developed in close relationship with ductal epithelial hyperplasia in both estradiol-treated rats and humans, but not in DMBA-treated rats.

• Keywords: Estrogen;Rat;Breast carcinoma;