COL1A1 and dermatofibrosarcoma protuberans: Based on the molecular mechanism of the COL1A1-PDGFB fusion, DFSP patients are often treated with a PDGFB receptor inhibitor, such as imatinib, but efficacy of this drug in a metastatic setting is still unclear because approximately 50% of metastatic DFSP cases show no response to imatinib [13–16].