Histopathogenesis of 7,12-diemthylbenz(a)anthracene-induced rat mammary tumors.

The histopathogenesis and growth behavior of mammary tumors and dysplasias induced by a single intragastric dose of 7,12-dimethylbenz[a]anthracene in 50-day-old virgin female Lewis rats were examined both in situ and after transplantation into gland-free mammary fat pads of syngeneic hosts. Terminal mammary ductules are indicated as a site of origin of both ovarian hormone-dependent mammary tumors and spontaneously gegressing mammary tumors, and terminal ductule hyperplasia appears to be an early stage in mammary tumor formation. The precancerous nature of hyperplastic alveolar nodules induced by dimethylbenzanthracene in rats has been further examined, and our studies indicate that these nodules are not significantly preneoplastic.