[477] EMA Expression in Epithelioid Benign Fibrous Histiocytoma.

Leona A Doyle, Christopher DM Fletcher. Brigham and Women's Hospital, Harvard Medical School, Boston

Background: Epithelioid Benign Fibrous Histiocytoma (EBFH) is considered a morphologic variant of cutaneous FH, but lacks many characteristic features of ordinary FH and the epithelioid cytomorphology may mimic other dermal neoplasms. Our personal experience of EMA expression in some cases of EBFH has added to the diagnostic difficulty. The aim of this study was to examine the immunohistochemical profile and incidence of EMA expression in a series of EBFH.
Design: 44 cases of EBFH with available unstained slides were retrieved from consultation files. Clinical, pathologic and immunohistochemical features were evaluated.
Results: 26 patients were female and 18 male; median age was 39 years (range 7-82). 24 tumors arose on the lower limbs, 12 on the upper limbs, 4 in the head and neck, 3 on the trunk and 1 on the vulva. Most tumors were exophytic with a well-formed collarette and mild epidermal hyperplasia. All were well circumscribed (3 had a focally infiltrative edge) and composed of a monomorphic intradermal proliferation of plump ovoid cells with a sheet-like and/or storiform growth pattern, perivascular accentuation and varying numbers of admixed smaller spindled cells. Tumor cells had vesicular nuclei, small nucleoli and abundant palely eosinophilic cytoplasm. Binucleate cells were present in all cases and scattered multinucleate giant cells in 17/44 (39%). 2 cases showed prominent nuclear atypia. The tumor stroma was variably loosely collagenous or hyalinized and lacked a significant inflammatory infiltrate. Metaplastic ossification was seen in 2 cases and prominent myxoid change in 2 cases. Membranous EMA positivity was found in tumor cells in 27/42 cases (64%); 22 showed focal, multifocal or diffuse positivity and 5 had only scattered positive cells. There were no significant morphologic differences between cases that expressed and those that did not express EMA. Focal positivity for Factor XIIIa was found in 10/14 (71%) and D2-40 in 14/27 (52%). Scattered SMA positive tumor cells were seen in 11/43 (25%). Focal positivity for claudin was found in 3/42 (7%). CD163 staining highlighted stromal macrophages; however, in 5 cases it was difficult to exclude focal staining in tumor cells. Tumor cells were consistently negative for pan-keratin, S100, CD34, CD68, desmin, p63 and CD31.
Conclusions: The high incidence of EMA expression in EBFH is an unexpected finding and is a potential diagnostic pitfall. The significance of this finding is unclear, but raises the possibility that EBFH is unrelated to ordinary FH. Other immunophenotypic findings make perineurial, epithelial or myoepithelial differentiation unlikely.
Category: Dermatopathology

Wednesday, March 2, 2011 1:00 PM

Poster Session VI # 121, Wednesday Afternoon


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