A case of dermatofibrosarcoma protuberans of the vulva with a COL1A1/PDGFBfusion identical to a case of giant cell fibroblastoma

Dermatofibrosarcoma protuberans (DFSP) is a highly recurrent low-grade soft tissue sarcoma, which is usually located on the trunk. Presentation in the vulva is rare, with only 13 cases being reported to date, none of which ha ve been investigated at the cytogenetic or molecular level. Specific cytoge netic abnormalities, involving chromosomes 17 and 22, are characteristic fe atures of DFSP and giant cell fibroblastoma (GCF), a tumor closely related to DFSP. These chromosomal rearrangements result in the fusion of the COL1A 1 and PDGFB genes in both lesions and show wide variation in the position o f the fusion point in COL1A1. Here, we describe a case of DFSP of the vulva with a typical monotonous storiform pattern, with no foci of multinucleate d giant cells. Cytogenetic analysis showed a 47,XX,+r karyotype in 50% of t he cells, and molecular investigation disclosed the presence of a transcrip t fusing COL1A1 exon 37 to PDGFB exon 2. This is the first case of DFSP sho wing such a fusion point, which is intriguingly identical to that found in a GCF case, indicating that the COL1A1/PDGFB fusion point position does not seem to affect tumor morphology. This finding further underlines the very close relationship between these two morphologically distinct entities.