[Comparative electron microscopic study of spontaneous and DMBA-induced tumors of mouse mammary glands]

The ultrastructural peculiarities of spontaneous and DMBA induced breast tumours in C3H/He and C3H/Sn mice are described. It is shown that spontaneous breast tumours in mice are highly differentiated adenocarcinomas arisen from acinus against a background of alveolar hyperplasia. DMBA induced breast tumours in mice develop with transformation of ductule-epithelial population of cells. The content and distribution of virus particles are different in spontaneous and DMBA induced breast tumours. The possible transformation of myoepithelial cells is suggested.