PDGFB and dermatofibrosarcoma protuberans: Furthermore, a fluorescence in situ hybridization (FISH) analysis was performed on formalin-fixed, paraffin-embedded biopsy tissue using the SPEC COL1A1/PDGFB Dual Color Dual Fusion Probe (ZytoVision, Bremerhaven, Germany), as the COL1A1-PDGFB (collagen type I alpha 1 chain-platelet-derived growth factor beta) gene fusion is observed in the vast majority of DFSP cases.