Dermatofibrosarcoma protuberans of the vulva and groin: Detection of COL1A1-PDGFB fusion transcripts by RT-PCR

Background: Dermatofibrosarcoma protuberans (DFSP) is an uncommon infiltrative tumor of the dermis with characteristic cytogenetic features, specifically the translocation t(17;22)(q22;q13) which often manifests as a supernumerary ring chromosome r(17;22). The translocation results in the fusion of two genes, collagen type I alpha 1(COL1A1) and platelet-derived growth factor B-chain (PDGFB). The trunk and extremities are the anatomic sites of predilection for DFSP, whereas the vulva and groin are quite uncommon sites of involvement. Methods: This investigation evaluated seven DFSPs (four vulvar and three groin) for the presence of COL1A1-PDGFB fusion transcripts by reverse transcriptase-polymerase chain reaction (RT-PCR), using archival formalin-fixed, paraffin-embedded tissue. Results: Six of seven cases (three vulvar, three groin) contained a COL1A1-PDGFB fusion transcript. Sequence analysis of the PCR products revealed that the break-point of the COL1A1 gene was located after exon 40 in two patients, after exon 42 in one patient, after exon 44 in one patient, and after exon 47 in two patients; the break-point in the PDGFB gene was before exon 2 in all cases. No fusion transcript could be amplified in one case. Conclusions: As in DFSP at other sites, COL1A1-PDGFB chimeric fusion transcripts are present in vulvar and groin DFSP. The transcripts can be detected in formalin-fixed, paraffin-embedded tumor tissues, and have the same general pattern of exon boundaries as in DFSP at other sites.