PDGFB rearrangement in dermatofibrosarcoma protuberans: correlation with clinicopathologic characteristics and clinical implications.

Dermatofibrosarcoma protuberans (DFSP) is characterized genetically by the translocation t(17;22)(q22;q13), which creates a COL1A1/PDGFB fusion gene. The implications of this gene for the clinicopathologic features of the disease are not fully understood. Fifty-one cases of DFSP from 46 patients were reclassified as DFSP (n=29) and DFSP-fibrosarcomatous variant (DFSP-FS; n=22). Fluorescence in situ hybridization was performed using a dual-color break-apart probe to detect rearrangements involving PDGFB, and CD34 immunohistochemistry staining was done. The DFSP-FS was found in older patients, and the tumors were larger, with a smaller mean area of staining for CD34. PDGFB rearrangement was found in 45 cases (95.7%). The mean gene copy number was 3.82 (range 2.2-6.45) and was higher in DFSP-FS than in classic DFSP (4.54 vs. 3.47; P < .001). The PDGFB copy number showed a moderate positive correlation with the number of mitotic figures and tumor size. Patients undergoing wide excision or having no involvement of the resection margin had no relapses. These results suggest a role for COL1A1/PDGFB in sarcomatous change in DFSP over time. Detection of COL1A1/PDGFB rearrangement by fluorescence in situ hybridization is useful for confirmation of the diagnosis. Patients who present with metastatic DFSP-FS show less typical histologic findings and loss of CD34 staining, leaving PDGFB rearrangement as the preferred adjunctive method for diagnosis from small biopsies and for prediction of the value of imatinib therapy.