Basal-like carcinoma of the breast: further evidence of the possibility that most metaplastic carcinomas may be actually basal-like carcinomas.

Some investigators have previously suggested that basal-like carcinoma may consist of components of invasive ductal carcinoma, not otherwise specified, metaplastic carcinoma, and medullary carcinoma. We report here two cases of breast carcinoma showing basal cell/myoepithelial differentiation. The first case was a 58-year-old Japanese woman and the second case was a 39-year-old Japanese woman. The two tumors were composed of the proliferation of epithelial cells and/or spindle-or stellate-shaped cells on the background of mucinous materials. Additionally, chondroid matrix was observed in the metastatic lesion of the first case and the primary lesion of the second case. Immunohistochemically, epithelial neoplastic cells were positive for E-cadherin and cytokeratin CAM5.2, and epithelial and spindle-or stellate-shaped cells were positive for cytokeratins 5, 14, or 17, alpha-smooth muscle actin, S-100, and p63. Our results supply further evidence that most metaplastic carcinomas may be actually be basallike carcinomas.