PDGFRA and gastrointestinal stromal tumor: In addition, the efficacy of reovirus against secondary imatinib-resistant GIST with acquired point mutations to KIT in exon 13, 14, and 17, which is detected in 40-80% of patients progressing on imatinib, and PDGFRA exon 18 mutation, identified in a subset of GIST refractory to imatinib [2, 19, 20, 35], is not clarified in this study.