EMA positivity in epithelioid fibrous histiocytoma: a potential diagnostic pitfall

Background: Epithelioid fibrous histiocytoma (EFH) represents a morphologic variant of cutaneous fibrous histiocytoma (FH) but can lack many characteristic features. The presence of epithelioid cytomorphology may mimic other dermal neoplasms. Our anecdotal experience of epithelial membrane antigen (EMA) expression in some examples of EFH has caused diagnostic difficulty. Our aim was to examine the immunohistochemical profile and incidence of EMA expression in EFH. Methods: Forty-four cases of EFH were retrieved from consultation files. Clinicopathologic and immunohistochemical features were evaluated. Results: Membranous EMA positivity was found in tumor cells in 27/42 cases (64%). Focal positivity for factor XIIIa was found in 10/14 (71%) and D2-40 in 14/27 (52%). Scattered smooth muscle actin (SMA)-positive tumor cells were seen in 11/43 (25%). Focal positivity for claudin-1 was found in 3/42 (7%). CD163 staining highlighted stromal macrophages; however, in five cases it was difficult to exclude focal staining of tumor cells. Tumor cells were consistently negative for pan-keratin, AE1/AE3, S100, CD31, CD34, CD68, desmin, p63, GFAP and CD45/LCA. Conclusion: Frequent EMA expression in EFH represents an unexpected finding and constitutes a potential diagnostic pitfall. Although of uncertain significance, this finding, when combined with established morphologic differences, raises the possibility that EFH is unrelated to classic FH.