Findings of myoepithelial cells in human breast cancer. Ultrastructural and immunohistochemical study by means of anti-myosin antibody.

Detailed light and electron microscopic, and immunohistochemical observations were made on the distribution and morphological characteristics of myoepithelial cells in the 53 cases of breast cancer. In non-invasive carcinoma, myoepithelial cells in the normal duct were found to be remaining at the outer margin of the cancer nests, but neoplastic myoepithelial cells were not detected in the carcinoma tissue. In invasive carcinoma, a small number of fluorescence-weakly-positive cells could be observed in more than 50% of medullary-tubular carcinoma, in all cases of papillary-tubular carcinoma, and two of three cases of invasive lobular carcinoma. Almost all of these cells were ultrastructurally intermediate cells which have the morphological characteristics of both epithelial cell and myoepithelial cell. Fluorescence-positive cells were observed in all cases of scirrhous carcinoma. Moreover, these cells showed a stronger fluorescence than that of other types of carcinoma and were ultrastructurally more similar to normal myoepithelial cell. The tumor cells having myoepithelial characteristics in invasive carcinoma showed a stronger tendency for arranging at the margin of carcinoma nests in contact with the stroma. The results of the present study indicate that in invasive carcinoma of the breast, neoplastic myoepithelial cells could be demonstrated together with ductal epithelial cells and as to its histogenesis, there is a possibility that breast cancer develops from common stem cells which have the ability of differentiating into both epithelial and myoepithelial cell because of the presence of intermediate cells.