Identification of t(17;22)(q22;q13) (COL1A1/PDGFB) in dermatofibrosarcoma protuberans by fluorescence in situ hybridization in paraffin-embedded tissue microarrays.

Dermatofibrosarcoma protuberans is genetically characterized by the translocation t(17;22)(q22;q13) resulting in the PDGFB/COL1A1 fusion gene. Fluorescence in situ hybridization with specific probes enables a rapid detection of this gene. In this study, the presence of the translocation t(17;22)(q22;q13) by fluorescence in situ hybridization in paraffin-embedded tissue microarrays was analyzed. Two tissue microarrays including 40 cases of dermatofibrosarcoma protuberans and 20 dermatofibromas were evaluated. Fluorescence in situ hybridization analyses were performed using a dual-color dual-fusion noncommercial probe. Clinical and histopathologic features were examined, and the association with fluorescence in situ hybridization results was assessed. A total of 29 samples of dermatofibrosarcoma protuberans and 16 of dermatofibromas were successfully evaluated. Twenty-five (86%) dermatofibrosarcoma protuberans samples were positive for the translocation, which was absent in all samples of dermatofibromas. Two of the negative dermatofibrosarcoma protuberans showed unusual, hypercellular areas with marked cytologic atypia, whereas 1 case exhibited overlap features with dermatofibroma. Tumors with fibrosarcomatous areas seemed to have a higher percentage of positive cells and the number of copies of the COL1A1/PDFGB gene. In conclusion, the COL1A1/PDGFB fusion gene was present in most of the dermatofibrosarcoma protuberans tissue samples. The detection of the translocation may be an additional diagnostic tool in cases of dermatofibrosarcoma protuberans showing nonconclusive histologic features.