Importance: Dermatofibrosarcoma protuberans (DFSP) is a rare skin cancer that develops in the deep dermis to subcutaneous adipose tissues. A COL1A1-PDGFB gene fusion, leading to the constitutive expression of PDGFB, is the tumorigenic mechanism in most DFSP cases.
Objectives: To evaluate the specificity of PDGFB expression as a diagnostic marker of DFSP and to determine whether other pathomechanisms (ie, gene fusions) exist in patients with DFSP without the COL1A1-PDGFB fusion gene.
Design, setting, and participants: All patients with DFSP registered in the pathologic database of the University of the Ryukyus from January 1, 1997, through December 31, 2013, and Gunma University from January 1, 1996, through December 31, 2011, were included in this analysis. Samples were obtained from 30 patients presenting with DFSP tumors. We examined the clinicopathologic characteristics and the expression of PDGFB, PDGFRβ, PDGFRα, CD34, nestin, factor XIIIa, fibronectin, α-smooth muscle actin, S-100 protein, and Ki-67 in 30 DFSP cases and 48 non-DFSP mesenchymal tumor cases by immunohistochemical analysis. We then analyzed tumor tissues for the presence of the COL1A1-PDGFB fusion gene. We also tested whether other genes enriched in fibroblasts formed fusion products with PDGFB by reverse transcription-polymerase chain reaction analysis, using gene-specific primers.
Main outcomes and measures: We aimed to analyze tumor tissues for the presence of the COL1A1-PDGFB fusion gene to investigate expression of PDGFB in DFSP tumors.
Results: PDGFB expression was detected in 28 (93%) of 30 patients with DFSP. PDGFB was not homogenously expressed in DFSP tumor cells, whereas CD34 and nestin were often expressed throughout the tumor mass. In 1 DFSP tumor, the COL1A1-PDGFB fusion gene was not detected even though PDGFB was expressed. We identified a novel COL1A2-PDGFB fusion gene in this tumor.
Conclusions and relevance: Our findings indicate that PDGFB protein is expressed in most DFSP tumors and may be a useful diagnostic tool when used in conjunction with CD34 and nestin expression analysis. These PDGFB expression data, in addition to our discovery of a novel PDGF fusion gene, strongly support the concept that DFSP is a PDGFB-dependent tumor type.