Key Inclusion Criteria:

1. Histologically confirmed locally advanced, metastatic, and/or unresectable GIST.  Molecular pathology report must be available for Part 2; if molecular pathology report
is unavailable or inadequate, an archival or fresh tumor tissue sample will be required to evaluate mutational status prior to randomization.

2. Documented disease progression on or intolerance to imatinib.

3. Subjects must have received the following treatment:

- Part 1a: Treatment with ≥1 prior lines of therapy for GIST;

- Part 1b: Treatment with ≥ 2 prior TKI for GISTs;

- Part 2: Prior treatment with imatinib only.

4. Have at least 1 measurable lesion according to mRECIST v1.1.

5. ECOG - 0 to 2.

6. Have clinically acceptable local laboratory screening results (clinical chemistry and hematology) within certain limits.

Key Exclusion Criteria:

1. Known PDGFR driving mutations or known succinate dehydrogenase deficiency.

2. Clinically significant cardiac disease.

3. Major surgeries (e.g., abdominal laparotomy) within 4 weeks of the first dose of study drug.

4. Gastrointestinal abnormalities including, but not limited to, significant nausea and vomiting, malabsorption, external biliary shunt, or significant bowel resection that would preclude adequate absorption.

5. Any active bleeding excluding hemorrhoidal or gum bleeding.

6. Seropositive for HIV 1 or 2, or positive for hepatitis B surface antigen or hepatitis C virus (HCV) antibody.

7. Active, uncontrolled, systemic bacterial, fungal, or viral infections at Screening.

8. Received strong CYP3A4 inhibitors or inducers.

9. Received sunitinib within 3 weeks (Part 1a, Part 1b).

Eligibility last updated 8/8/23. Questions regarding updates should be directed to the study team contact.