Track

Case Reports

Abstract

Dermatofibrosarcoma protuberans (DFSP) is an uncommon, low-grade sarcoma that typically arises in the dermis or superficial subcutis. We report a rare case of DFSP originating exclusively from deep soft tissue with invasion to the vertebral bone, without any dermal or subcutaneous involvement, confirmed by molecular testing. A middle-aged patient presented with subacute right flank pain. Physical examination revealed no overlying skin changes or palpable masses. Initial radiographs were unremarkable. Subsequent cross-sectional imaging (CT and MRI) identified a 4.2 cm soft tissue mass in the paraspinal musculature at the T7 level. CT-guided core needle biopsy showed a low-grade spindle cell neoplasm with features suggestive of DFSP. Immunohistochemistry demonstrated diffuse CD34 positivity. Fluorescence in situ hybridization (FISH) revealed a rearrangement involving the PDGFB gene region, with loss of the 5’PDGFB probe and retention of the 3’PDGFB probe, confirming the diagnosis. After initial response to Imatinib, the tumor grew rapidly and was surgically resected with negative margins. However, it recurred within a year with fibrosarcomatous transformation. DFSP typically exhibits infiltrative growth into the dermis and subcutis, with characteristic storiform histology and often a COL1A1-PDGFB fusion. To our knowledge, this is the first published case of DFSP originating entirely within deep paraspinal muscle with extension into the vertebral bone without involvement of overlying skin, dermis, or subcutaneous fat. This case expands the known anatomic spectrum of DFSP and highlights the critical role of molecular diagnostics in establishing the diagnosis in atypical presentations.