A proposed selective cell carcinogenesis in mammary tumors.

The present study was done to ascertain whether a specific carcinogenic agent has a causal effect on the initial proliferation of only one cell type or whether it acts indiscriminately on all cells in the breast secretory unit. Enzymes histochemistry and electron microscopy were performed on DMBA-induced mammary tumors in female Sprague-Dawley rats and on virus-associated spontaneous mammary tumors in C3H/HEJ mice. The results showed that the chemical carcinogen DMBA affects initial myoepithelial cell proliferation, while virus-associated mammary carcinoma originated from ductular epithelial cell proliferation. To determine whether a specific tumor is composed of a single cell type, tumors were grown in tissue culture. The monolayer was fixed in the usual manner for electron microscopy while in Falcon tissue culture plates. The plates were dissolved in xylene and the monolayer was cut into small pieces and embedded in the plastic media. Electron microscopy performed on the tissue culture and the original tissue from the virus-induced tumors showed the presence of viruses in large numbers. It also suggested the differentiation of basal membrane to form basal lamina and apical plasma membrane into microvilli. This study strongly suggests the presence of selective cell carcinogenesis in the mammary gland.