Inclusion Criteria

• Male or female, of any racial or ethnic group
• Age 18 years or older
• Life expectancy of greater than 12 weeks
• Patient able and willing to provide informed consent
• Normal liver function, defined as AST and ALT ≤2.5x ULN, and Total Bilirubin ≤ 2x ULN.
• Total creatinine ≤ 1.5x ULN
• ECOG Performance Status 0 - 2 (Appendix II)
• Patients must have histologically or cytologically confirmed GIST with a D842-related mutation or deletion on the PDGFRA gene
• 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) as >20 mm with conventional techniques or as >10 mm with spiral CT scan. See Section 10.1.2 for the evaluation of measurable disease.
• Patients may have received prior chemotherapy or radiation therapy. Patients must have recovered from any prior therapy and at least 4 weeks must have elapsed since prior treatment.

Exclusion Criteria

• Patient unable to provide informed consent
• ECOG Performance status > 2
• Any concurrent anticancer therapy, immunotherapy, or hormonal therapy.
• Any other investigational agents within 4 weeks of start of study drug
• Patients with known or active Hepatitis B or C; liver cirrhosis.
• Patients with active fungal, viral, and bacterial infections
• Positive serum pregnancy test
• Pregnant or lactating women
• Patients on concomitant medications that induce or inhibit CYP3A4 (Appendix III)
• Patients on proton pump inhibitors
• Patients with severe and/or uncontrolled concurrent medical disease that in the opinion of the investigator could cause unacceptable safety risks or compromise compliance with the protocol e.g. impairment of gastrointestinal (GI) function, or GI disease that may significantly alter the absorption of the study drugs