Subcutaneous dermatofibrosarcoma protuberans, a rare subtype with predilection for the head: A retrospective series of 18 cases

BackgroundDermatofibrosarcoma protuberans (DFSP) typically affects the dermis and subcutaneous tissue. The subcutaneous variant is rare.ObjectiveWe sought to characterize the subcutaneous DFSP (SC-DFSP) variant and compare it with cutaneous DFSP (C-DFSP).MethodsThis work was a retrospective study of DFSP treated in our institution.ResultsOf 124 cases of DFSP, 18 were SC-DFSP (14.5%). Except for the deep location, the pathologic and genetic features were indistinguishable from the C-DFSP variant. Histologically, of 18 SC-DFSP cases, 13 were classic DFSP, 3 fibrosarcomatous DFSP (FS-DFSP), 1 Bednar tumor, and 1 giant-cell fibroblastoma. All tumors expressed CD34 and the COL1A1-PDGFB fusion transcripts. In our series, higher proportions of SC-DFSP tumors (61%) than C-DFSP tumors (8.5%) were located on the head (P < .001). Of the 20 DFSP tumors on the head (16.1%), 11 were SC-DFSP and 9 were C-DFSP.In addition, half the SC-DFSP tumors affected muscle or periosteum, compared with a quarter of the C-DFSP tumors (P = .009). SC-DFSP needed a higher number of Mohs stages than did C-DFSP (P = .009). Median follow-up time was 63 months, and 2 FS-DFSP tumors recurred (1 SC-DFSP, 1 C-DFSP).LimitationsLimitations include the retrospective aspect of the study.ConclusionsMost DFSP tumors involving the head were subcutaneous and required more complex surgery. Dermatologists should be aware of this atypical presentation, especially in lesions involving the head.