KIT and gastrointestinal stromal tumor: Among GIST cases, mutations in the c-kit gene are the most common, with exon 11 mutations present in 70%–80% of cases.16)KIT exon 9 mutations are associated with a higher response rate to sunitinib (58%) and significantly longer progression-free survival compared with exon 11 mutations.17–19) In this case, the presence of a KIT exon 9 mutation is consistent with the favorable response to sunitinib.