- Male or female patients ≥ 18 years of age -WHO performance status (PS) of 0-2 -Histologically confirmed diagnosis of GIST that is unresectable or metastatic -.Available tissue specimen: • Dose-escalation part: patients must have available archival tumor tissue which can be shipped during the course of the study. In the absence of archival tumor tissue, patients must agree to a fresh pre-treatment biopsy at screening. • Dose-expansion part: patients must have available archival tumor tissue which can be shipped during the course of the study and must agree to a fresh pre-treatment biopsy