Lymphoepithelioma-like carcinoma of the breast. An unusual pattern of infiltrating lobular carcinoma.

A case of breast carcinoma, showing both lymphoepithelioma-like and lobular infiltrating carcinoma, is described, which must be distinguished from the medullary carcinoma with which it shares some features, such as the strong lymphocytic infiltration, but not sharp circumscription, syncytial growth pattern, nuclear pleomorphism, and high mitotic rate. Unlike the lymphoepithelial carcinoma of the nasopharynx and some lympho-epithelioma-like carcinomas of the lung, stomach, salivary glands, and thymus, it does not seem to be connected with Epstein-Barr virus (EBV) infection, as shown by negative results of both in situ hybridization and polymerase chain reaction. This neoplasia may be defined as a peculiar form of lobular carcinoma, therefore, more representative of an unusual microscopic pattern than a distinctive clinicopathologic entity in itself.