[558] Desmin and CD34 Positivity in Cellular Benign Fibrous Histiocytoma: An Immunohistochemical Analysis of 100 Cases

Elgida R Volpicelli, Christopher DM Fletcher. Brigham and Women's Hospital and Harvard Medical School, Boston, MA

Background: Cellular benign fibrous histiocytoma (CBFH) represents a morphologic variant of cutaneous fibrous histiocytoma (FH) and accounts for about 5 percent of cases. Because of it relative monomorphism and fascicularity CBFH can easily be mistaken for a malignant lesion. In fact, while smooth muscle actin (SMA) positivity is common and a reassuring finding in CBFH, CD34, often used to distinguish CBFH from dermatofibrosarcoma protuberans (DFSP) can also be positive. To add to the confusion, desmin positivity may also be observed in a subset of CBFH. Desmin and CD34 positivity often seem to cause diagnostic difficulty and may lead to misdiagnosis. Our aim was to examine the immunohistochemical profile and incidence of desmin and CD34 expression in CBFH.
Design: 100 consecutive cases of morphologically typical CBFH were retrieved from consultation files. Clinicopathologic and immunohistochemical features were evaluated.
Results: Cytoplasmic SMA positivity was found in tumor cells in 93/100 cases (93%). Desmin positivity was found in 32% of the cases. Out of these 32 cases, 14 showed multifocal positivity, 9 showed focal positivity, 8 showed scattered cells, and 1 showed diffuse positivity for desmin. CD34 was positive in 6/100 cases (6%), with 1 being diffusely positive, 3 showing multifocal positivity and 2 showing focal positivity. More often there were entrapped CD34-positive dermal fibroblasts interdigitated with tumor at its periphery. There was no evident correlation between immunophenotype and anatomic site or other clinical variables.
Conclusions: Frequent desmin (32%) and occasional CD34 (6%) expression are encountered in CBFH. Desmin positivity can be explained on the basis of myofibroblastic differentiation in CBFH. The occasional CD34 positivity in a subset of CBFH should not be a deterrent from making the correct pathologic diagnosis, based on characteristic morphologic features.
Category: Dermatopathology

Monday, March 19, 2012 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 83, Monday Morning

 

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