Epithelial membrane antigen staining patterns of histiocytic lesions.

Epithelial membrane antigen (EMA) appears to be a marker of activation, proliferation, and/or neoplasia in some epithelial and nonepithelial cells, including histiocytes. We performed immunoperoxidase stains for EMA on a variety of histiocytic lesion specimens, including specimens from two cases of interdigitating reticulum cell lymphoma, 12 cases of histiocytosis X, seven cases of sarcoidosis, five cases of granuloma annulare, 13 juvenile xanthogranulomas, two reticulohistiocytomas, five xanthelasmas, three dermatopathic lymph nodes, and three foreign body reactions. Only the two cases of interdigitating reticulum cell lymphoma and two of the 12 cases of histiocytosis X exhibited significant EMA positivity. These findings may prove useful in the differential diagnosis of histiocytic lesions.