Pathology of early lesions of mammary carcinoma and mammary dysplasia induced by 7,12-dimethylbenz(a)anthracene in the neonatally androgenized Sprague-Dawley female rats

Summary

Female Sprague-Dawley rats were neonatally androgenized by giving subcutaneous injections of 1.25 mg of testosterone propionate at 2 days of age and were also given 20 mg of 7,12-dimethylbenz(a)anthracene at 50 days of age. These androgenized rats were divided into 2 groups. Group I was for the induction of mammary dysplasia. Group II was for the induction of mammary carcinoma, in which the rats received daily intramusclar injections of 4 mg of progesterone beginning 14 days after carcinogen administration. To detect early lesions, the mammary glands of rats in both groups were examined grossly and histologically at regular intervals. The incidences of solid masses of mammary dysplasia with microscopic characteristics of acinar and fibrotic adenosis, of gross cystic mammary dysplasia and of mammary carcinoma were 91.7%, 70.6% and 5.8% in Group I, and 51.6%, 0% and 93.8% in Group II, respectively. Three kinds of microscopic lesion were detected in the mammary glands of 106-day-old rats; nodular acinar adenosis with a large lobular structure composed of numerous acini, microcysts with milky eosinophilic secretion in the lumina and atypical nodular ductal hyperplasia. The incidences of these three lesions were 68.4%, 68.4% and 0% in Group I, and 12.2%, 0% and 15.0% in Group II, respectively. This close agreement between the incidence of palpable and microscopically detectable lesions indicates that acinar adenosis and atypical ductal hyperplasia may represent the early changes of 7,12-dimethylbenz(a)anthracene-induced mammary dysplasia and mammary carcinoma respectively. Cyst formation appears to be due to the continued accumulation of milky secretion.