Ultrastructure of the hormone-dependent N-nitrosomethylurea-induced mammary carcinoma of the rat.

Hormone dependency of the N-nitrosomethylurea-induced mammary tumor in rats has been demonstrated by ovariectomy. Tumors showing a clear reduction in size in response to ovariectomy have been used in an ultrastructural study. Histologically, the tumor is an adenocarcinoma. The multilayered tumor parenchyma contains myoepithelial cells and highly and less-well-differentiated cells. The adluminal cells tended to be the most differentiated and were secretory in nature. After ovariectomy, junctional complexes of the luminal cells showed little change, but intercellular adhesion among the less-well-differentiated cells appeared weakened by the altered endocrine milieu; consequently, the parenchyma appeared less compact. Cellular degeneration occurred randomly and affected all cell types. However, the least affected cells were the poorly differentiated cells with a high nuclear-cytoplasmic ratio and few cytoplasmic organelles. The findings suggest that the latter may be the hormone-independent cell subpopulation in the N-nitrosomethylurea-induced mammary tumor.