Epithelioid sarcoma and isolated necrobiotic granuloma: a comparative immunocytochemical study.

Epithelioid sarcoma (ES) occasionally may be confused, both clinically and histologically, with isolated necrobiotic granulomas (ING), leading to misdiagnosis and potential mismanagement of these conditions. We studied 11 cases of ES and 11 of ING (6 examples of deep granuloma annulare and 5 of rheumatoid nodule) immunohistochemically, in an attempt to determine whether they could be diagnostically separated by such means. Monoclonal antibodies to cytokeratin polypeptides (CK), epithelial membrane antigen (EMA), and leukocyte common antigen (LCA) were applied to formalin-fixed, paraffin-embedded sections in each case, using the avidin-biotin-peroxidase complex technique. All ES cases stained positively for CK, and 6 expressed EMA, while examples of ING were non-reactive for these antigens. Conversely, the large epithelioid histiocytic cells in cases of ING were immunoreactive with anti-LCA, whereas no case of ES displayed this determinant in tumor cells. In the latter lesions, reactive peritumoral inflammatory cells were LCA-positive, but were readily distinguished from neoplastic cells on morphological grounds, as well as by their negativity with anti-CK and anti-EMA. Based on these data, it is concluded that immunohistologic stains for epithelial and hematopoietic antigens are valuable in the conclusive diagnostic separation of epithelioid sarcoma and necrobiotic granulomas.