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Case ReportsAbstract
EWSR1::SMAD3 rearranged fibroblastic tumor is a recently described entity with only 19 cases reported in the literature thus far. Herein we present a case of EWSR1::SMAD3 rearranged fibroblastic tumor, adding to the histopathologic spectrum. A 44-year-old male presented with a 0.7 cm pink papule on the left scapular back, which had reportedly undergone prior partial biopsy with recurrence. Excisional biopsy was performed. Histopathology revealed a mostly circumscribed, asymmetric dermal epithelioid proliferation. The upper and mid dermis component was characterized by short fascicles and individual neoplastic cells, while the deeper portion showed epithelioid and to a lesser extent spindled cells extending between collagen bundles in a desmoplastic fashion. Most of the cells contained moderately large nuclei and increased amounts of amphophilic cytoplasm. Immunohistochemistry showed strong ERG positivity in most of the cell population. Immunostains showed many cells positive with B-catenin and retained positivity to BAP1, with some cells positive with p16, SMA, CD34, and a smaller number with CD31. Melan-A, SOX-10, S-100, EMA, CK, PRAME, and ALK immunostains were negative. Fluorescence in-situ hybridization (FISH) was performed using an EWSR1 (22q12) break-apart probe, demonstrating a population of cells with EWSR1 rearrangement (26% of interphase cells). Taken in combination with the morphologic changes, the findings were consistent with EWSR1::SMAD3 rearranged fibroblastic tumor. This case is the first reported on a non-extremity anatomical location and is unique in its prominent epithelioid cytomorphology; moreover, it lacks the hyalinized zones that have frequently been reported.