PDGFRA and gastrointestinal stromal tumor: Post hoc analyses revealed patients with KIT exon 11 mutation had better response to imatinib therapy compared to those with KIT exon 9.24,47 A meta-analysis of both phase III trials showed that patients with KIT exon 9 mutation who received high-dose imatinib had 42% higher median PFS and numerically, but not significantly better OS.25 Patients with PDGFRA D842V and without KIT or PDGFRA mutant GIST were confirmed imatinib nonresponders.24,25,34,47