⁃ Patients must have measurable disease, defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded for nonnodal lesions and short axis for nodal lesions) as≥10 mm (≥1 cm) with CT scan, MRI, or calipers by clinical exam.

• Age ≥18 years.

• Histologic diagnosis of GIST with presence of KIT exon 17, 18, or 14 mutation, or SDHB deficiency on tumor biopsy and/ or liquid biopsy.

• Participants must have unresectable or metastatic GIST and radiologic progression on imatinib treatment. Imatinib treatment must have been discontinued at least 5 days prior to the first dose of study drug. All imatinib treatment will be counted as 1 line of therapy.

• ECOG performance status ≤2 (Karnofsky ≥60%) at screening.

• Life expectancy of at least 12 weeks (3 months).

• Subjects must be able to understand and be willing to sign the written informed consent form. A signed informed consent form must be appropriately obtained prior to the conduct of any trialspecific procedure.

• Patients must have adequate organ and marrow function as definedbelow:

⁃ Hemoglobin ≥8 g/dL Absolute neutrophil count ≥1,000/mcL Platelets ≥100,000/mcL Total bilirubin ≤2 x institutional upper limit of normal (ULN) or \<3 x ULN in the presence of Gilbert's Disease AST and ALT ≤3 × institutional ULN ALT and AST ≤ 2.5 x ULN (≤ 5 x ULN for subjects with liver involvement of their cancer) Alkaline phosphatase ≤ 2.5 x ULN (≤ 5 x ULN for subjects with liver involvement of their cancer) Serum creatinine ≤ 3 x the ULN or 24-hr creatinine clearance \>30 ml/min (Cockcroft formula) INR/ PTT ≤ 1.5 x ULN. (Subjects who are prophylactically treated with an agent such as warfarin or heparin will be allowed to participate provided that no prior evidence of underlying abnormality in coagulation parameters exists. Close monitoring of at least weekly evaluations will be performed until INR/PTT is stable based on a measurement that is pre-dose as defined by the local standard of care

• Women of childbearing potential must have a negative serum pregnancy test performed within 7 days prior to the start of study drug. Post-menopausal women (defined as no menses for at least

• 1 year) and surgically sterilized women are not required to undergo a pregnancy test.

• Subjects (men and women) of childbearing potential must agree to use adequate contraception beginning at the signing of the ICF until at least 2 months after the last dose of study drug.

⁃ Approved methods of birth control are as follows: Hormonal contraception (i.e. birth control pills, injection, implant, transdermal patch, vaginal ring), Intrauterine device (IUD), Tubal Ligation or hysterectomy, Subject/Partner post vasectomy, Implantable or injectable contraceptives, and condoms plus spermicide. Not engaging in sexual activity for the total duration of the trial and the drug washout period is an acceptable practice; however periodic abstinence, the rhythm method, and the withdrawal method are not acceptable methods of birth control. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately

⁃ • Subject must be able to swallow and retain oral medication.