2. Patients in Cohort A must have evidence of activation mutations in exon 11 of KIT in their tumors. Demonstration of an exon 11 mutation may be based on prior assessment or on evaluation of a tumor sample after enrollment in this study. Patients in Cohort B must have GIST that lacks activating mutations in KIT exon 11, but may have evidence of another activating mutation such as in KIT exon 9 or in PDGFR-α. Patients may be enrolled in the study prior to determination of the appropriate cohort (as long as both cohorts are open for enrollment).