Lymphoepithelioma-like carcinoma of the breast.

Lymphoepithelioma describes an undifferentiated carcinoma of the nasopharyngeal region characterized by a pronounced reactive lymphocytic infiltrate, often obscuring the neoplastic epithelial component. In recent years, histologically similar lesions have been reported in a number of other sites. We report such a lesion in the breast of a 65-yr-old woman; this site of involvement has not previously been described. The unusual histologic appearance raised other diagnostic possibilities and was a dilemma on frozen section. Immunostains for epithelial markers were particularly useful in delineating the scant epithelial neoplastic elements among the abundant lymphocytic component. In situ hybridization for Epstein Barr viral DNA was negative.