Inclusion Criteria:

          1. Patient has pathologically confirmed SDH-mutant/deficient GIST.

          2. Has recovered from the acute toxic effects of all prior chemotherapy, immunotherapy,
             or radiotherapy.

          3. Patient has an ECOG Performance Status of 0-2.

          4. Patient has adequate hematologic, hepatic and renal function.

          5. Female patient of childbearing potential has a negative serum or urine pregnancy
             within 72 hours prior to receiving the first dose of study medication.

          6. Female patient of childbearing potential agrees to use 2 methods of birth control or
             be surgically sterile, or abstain from heterosexual activity for the course of the
             study through 120 days after the last dose of study medication.

          7. Male patient with a partner of childbearing potential agrees to use an adequate method
             of contraception starting with the first dose of study therapy through 120 days after
             the last dose of study therapy.

          8. Has measurable or evaluable disease as per RECIST v1.1 (Appendix B).

          9. Life expectancy of >12 weeks.

        Exclusion Criteria:

          1. Patients who have had major surgery within 4 weeks of initiation of study medication.

          2. Patients who are receiving other concurrent anti-neoplastic therapy (e.g.,
             chemotherapy, targeted therapy, immunotherapy, or radiotherapy) at the start of study
             treatment.

          3. Patients with known brain metastases should be excluded from this clinical trial
             because of their poor prognosis and because they often develop progressive neurologic
             dysfunction that would confound the evaluation of neurologic and other adverse events.

          4. Evidence of severe or uncontrolled systemic diseases [e.g., unstable or uncompensated
             respiratory, cardiac (including life threatening arrhythmias)].

          5. Unresolved toxicity ≥ CTCAE Grade 2 from previous anti-cancer therapy except alopecia
             (if applicable) unless agreed that the patient can be entered after discussion with
             the Medical Monitor.

          6. Presence of cardiac impairment class III and IV definitions; OR history of myocardial
             infarction/active ischemic heart disease within one year of study entry; OR
             uncontrolled dysrhythmias; OR poorly controlled angina.

          7. Pregnant or breast-feeding females.

          8. Medical condition such as uncontrolled infection (including HIV), uncontrolled
             diabetes mellitus or cardiac disease which, in the opinion of the treating physician,
             would make this protocol unreasonably hazardous for the patient.

          9. Any concurrent condition which in the investigator's opinion makes it undesirable for
             the subject to participate in this trial or which would jeopardize compliance with the
             protocol.

         10. Patients who cannot swallow oral formulations of the agent