Invasive micropapillary carcinoma of the breast: an immunohistochemical study of neoplastic and stromal cells.

A 59-year-old woman complained of a palpable mass in the right breast, and a needle biopsy disclosed small clusters of neoplastic cells in the fibrous stroma. The small clusters did not contain fibrovascular cores but exhibited micropapillary configuration. Epithelial membrane antigen (EMA) immunohistochemistry confirmed the reverse polarity of the neoplastic cells. Additionally, the plasma membrane of many neoplastic cells stained with E-cadherin and beta-catenin. Myofibroblasts, which were positive for alpha smooth muscle actin (ASMA) and negative for cytokeratin 14, were abundant in the neoplastic stroma, but no CD34-positive stromal cells were observed in the neoplastic stroma. For comparison, 3 additional cases of invasive micropapillary carcinoma (IMC) and 4 cases of invasive ductal carcinoma (IDC) were studied. Similar results for stromal cells were obtained in all cases. Our results from this preliminary investigation suggest that CD34-positive stromal cells may disappear from the stroma of IMC as well as IDC.