Sclerosing Dermatofibrosarcoma Protuberans Shows Significant Overlap With Sclerotic Fibroma in Both Routine and Immunohistochemical Analysis: A Potential Diagnostic Pitfall

Abstract: Dermatofibrosarcoma protuberans (DFSP) is an uncommon, low-to-intermediate grade sarcoma with several histologic variants, including pigmented (Bednar tumor), sclerosing, myxoid, atrophic, and DFSP with fibrosarcomatous changes. Two patterns of sclerosis in DFSP can be observed, a sclerotic fibroma-like pattern and a morphea/lichen sclerosus-like pattern. Partial biopsies of sclerosing DFSPs with the sclerotic fibroma pattern can be misdiagnosed as sclerotic fibroma or other benign sclerosing tumors (eg, perineurioma, dermatofibroma). DFSPs from our tissue archives were screened for tumors with a sclerosing pattern, and then studied with epithelial membrane antigen (EMA), CD34, and elastic tissue staining to investigate whether such stains can differentiate sclerosing DFSP from sclerotic fibroma. Ten cases of sclerotic fibroma were similarly studied. Two of the 27 DFSPs were predominantly sclerosing and 5 additional DFSPs had a mixed histopathologic pattern including a sclerosing component. Immunohistochemically, all DFSPs with sclerosing (predominant or mixed) pattern were positive for CD34, and 5/7 were at least focally positive for EMA. Elastic tissue staining was reduced or absent in the sclerotic areas. All cases of sclerotic fibroma were either positive or focally positive for CD34, whereas EMA was focally positive in 5/10. Elastic tissue staining ranged from reduced to totally absent in the sclerotic fibromas. In conclusion, the similar histopathologic and immunophenotypic characteristics in sclerotic fibroma and sclerosing DFSP found in this analysis highlight the importance of obtaining clinical information and potentially additional excision for partial biopsies showing a sclerotic fibroma-like pattern.

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