PDGFB Rearrangements in Dermatofibrosarcoma Protuberans of the Vulva: A Study of 11 Cases Including Myxoid and Fibrosarcomatous Variants

Dermatofibrosarcoma protuberans (DFSP) is a low-grade fibroblastic sarcoma that tends to arise in young to middle age adults and involve the trunk and proximal extremities. Rare examples of vulvar DFSP have been reported, including myxoid, myoid, and fibrosarcomatous variants, but detection of the characteristic t(17;22)(q22;q13) that produces COL1A1-PDGFB gene fusion has not been evaluated in a large series of primary vulvar tumors. The clinical, morphologic, immunohistochemical, and molecular cytogenetic features of 11 cases were examined. Patient age ranged from 29 to 75 yr (mean, 46 yr; median, 43 yr). Seven tumors were purely classic DFSP, 1 was purely myxoid DFSP and the remaining 3 had varying quantities of fibrosarcomatous DFSP. All cases of classic DFSP had diffuse expression of CD34 and low-level p53 immunoreactivity. Myxoid variants had strong, but reduced expression of CD34. Fibrosarcomatous DFSP showed focal CD34 expression and increased p53 reactivity. Nine of 11 tumors (82%) had rearrangement of PDGFB by fluorescence in situ hybridization. The 2 nonrearranged tumors were a classic DFSP and a myxoid DFSP with fibrosarcomatous transformation. Follow-up was available for 9 patients (82%) and ranged from 1 to 108 mo (mean, 30 mo; median, 21 mo). Eight patients had tumors with positive margins, one of which developed local recurrence after no further therapy. No patient developed metastasis. The high frequency of PDGFB rearrangement in vulvar DFSP provides a useful exploit in diagnostically challenging cases and genetic evidence of probable clinical response to targeted therapeutics in cases of locally advanced or metastatic tumors.