Ultrastructure of the periductal area of comedo carcinoma in situ of the breast.

We have previously shown that the different biological natures of comedo ductal carcinoma in situ (DCIS) and non-comedo DCIS may, in part, be explained by the different expression patterns of tenascin, a large extracellular matrix protein, as observed by immunohistochemical studies. In the present study, we compared 8 cases of comedo DCIS with 5 cases of non-comedo DCIS by ultrastructural analysis, focusing on the myoepithelium, basal lamina, and tenascin-positive extracellular periductal stromal matrix. Our observations show that the comedo type DCIS frequently has an altered basal lamina, a looser and more disorganized collagenous matrix, and a general increase in stromal cellularity, including fibroblasts, lymphocytes, histiocytes and small blood vessels. In addition, in comedo DCIS, the lateral intercellular spaces between large myoepithelial cells that border the basal lamina are often expanded, compared to those of non-comedo DCIS. These results identify structural characteristics of comedo DCIS that may play a role in its greater preinvasive potential. They may also provide a structural basis for the different strategies that are needed for for clinical management of comedo DCIS, compared to non-comedo DCIS.