⁃ Age 20 years or older, at the time of acquisition of informed consent

⁃ Histologically confirmed metastatic and/or advanced GIST with CD117(+), DOG-1(+), or mutation in KIT or PDGFRα gene

⁃ P-glycoprotin IHC score \> 3 (Tumor tissue with disease progression after regorafenib treatment)

⁃ Failed (progressed and/or intolerable) after prior treatments for GIST, including at least imatinib and sunitinib, regorafenib.

⁃ Eastern Cooperative Oncology Group (ECOG) performance status 0 \

• 2

⁃ Resolution of all toxic effects of prior treatments to grade 0 or 1 by NCI-CTCAE version 5.0

⁃ At least one measurable lesion as defined by RECIST version 1.1.

⁃ Adequate bone marrow, hepatic, renal, and other organ functions Neutrophil \>1,500/mm3 Platelet \> 100,000/mm3 Hemoglobin \>8.0 g/dL Total bilirubin \< 1.5 x upper limit of normal (ULN) AST/ALT \< 2.5 x ULN Creatinine \<1.5 x ULN

⁃ Life expectancy \> 12 weeks

⁃ Washout period of previous TKIs or chemotherapy for more than 4 times the half life ((Imitinib and regorafenib need 1 week and sunitinib need 2 weeks.)

⁃ Provision of a signed written informed consent