PDGFD-Rearranged Dermatofibrosarcoma Protuberans With S100 and Pan-TRK Expression

Dermatofibrosarcoma protuberans (DFSP) is a fibroblastic malignancy characterized in most cases by COL1A1::PDGFB fusion. Rare cases exhibit alternative rearrangements involving PDGFD. Here, we describe a female patient in her third decade of life who presented with a spindle cell proliferation on the shoulder. Expression of pan-TRK and S100, together with absence of PDGFB overexpression, supported an initial impression of NTRK-rearranged spindle cell tumor. However, molecular analysis revealed PDGFD rearrangement, and re-excision demonstrated classic DFSP morphology in the residual tumor. Our findings underscore the importance of continued consideration for DFSP in tumors with focal S100 expression.