PDGFRB and sarcoma: However, the response rates of other sarcomas have mostly been poor.164 Indeed, a phase II clinical trial which assessed the performance of imatinib on 22 metastatic or relapsed KIT- or PDGFR-positive sarcomas only showed partial response in a single patient.165 Therefore, there was no correlation between the response to imatinib and expression levels of PDGFR/KIT.