A Study to Assess DCC-2618 and Sunitinib in Patients With Advanced GIST After Treatment With Imatinib

Inclusion Criteria: * Male or female patients ≥18 years of age. * Histological diagnosis of advanced GIST and capability of providing tumor tissue sample (the interval between tumor tissue collection and signing of informed consent form should be less than 3 years). Otherwise, biopsy is required. * Provide molecular test report with KIT/PDGFRA mutation status prior to randomization. * Patients must have progressed on imatinib or have documented intolerance to imatinib. Subjects must have discontinued imatinib treatment 10 days prior to the first dose of the study drug. All prior imatinib treatments will be considered as first-line (such as imatinib adjuvant therapy and imatinib dose increase). * ECOG PS of 0-2. * Female patients of childbearing potential must have a negative serum beta-human chorionic gonadotropin (β-hCG) pregnancy test at screening. * Patients of reproductive potential must agree to follow the contraception requirements. * At least 1 measurable lesion according to the "RECIST v1.1-GIST-specific Criteria" (non-nodal lesions must be ≥1.0 cm in the long axis or ≥ double the slide thickness in the long axis) ; obtaining radiographic image results within 28 days prior to the first dose of study drug. * Good organ function and bone marrow reserve function, including: * Neutrophil count ≥ 1,000/µL * Hemoglobin ≥ 8 g/dL * Platelet count ≥ 75,000/µL * Total bilirubin ≤ 1.5 × the upper limit of normal (ULN) * AST and ALT ≤ 3×ULN, and AST and ALT≤ 5×ULN in …