The GIST-RX1 model harboring KIT exon 11 and 17 (p.D816E) mutations established from a patient who showed clinical progression after treatment with imatinib, sunitinib, and sorafenib, showed resistance to imatinib and sunitinib, but modest antitumor effect with regorafenib. This evidence concerns the gene KIT and gastrointestinal stromal tumor.