Pathogenesis of Mammary Carcinomas Induced in Rats by 7, 12-Dimethylbenz[a]anthracene2

Abstract

The pathogenesis of mammary carcinomas was studied in Spragu-Dawley virgin female rats after gastric Instillation of 7,12-dimethylbenz[a]anthracene (DMBA) at 55 days of age. Nine rats were killed weekly, from the time of DMBA inoculation until the 15th week after treatment. All the glands of each animal were studied in both cleared wholemounts and paraffin sections. The earliest observed lesion was hyperplasia of the end-bud epithelium, which appeared as a multifocal phenomenon as early as 14 days post Inoculation. Intraductal proliferation of end buds evolved to intraductal carcinomas, which formed either cribriform or papillary patterns. Every carcinoma observed was ductal in origin. Differentiation of the alveolar portion of the gland led to adenomas, hyperplastic alveolar nodules, and cysts. The presence of the terminal end buds at the time of DMBA administration was considered to play an important role in the genesis of carcinomas.