KURA KO-MEN-015 Advanced Gastrointestinal Stromal Tumors

This study will have 3 parts: Dose Escalation, recommended Phase 2 dose (RP2D), and Dose Expansion. If you choose to join this study, the part in which you participate will depend on when you join the study. Dose Escalation: The main purpose of the Dose Escalation part is to determine 2 dose levels of the study drug to be further studied in combination with imatinib. Up to 4 different dose levels of the study drug are planned to be given to study participants in combination with imatinib. RP2D Determination: The main purpose of the RP2D Determination part is to find the most appropriate dose of the study drug in combination with imatinib. If you are enrolled in this part of the study, you will be dosed with the study drug at 1 of the 2 doses chosen from the Dose Escalation part to help identify the most favorable dose of the study drug. Dose Expansion: Participants will be enrolled in the Dose Expansion part of the study once the recommended combination dose level has been determined to be safe. If you are enrolled in this part of the study, you will get the study drug at the recommended dose level to further study how well it works with imatinib. Your participation in the study may last for up to 2 years, but it will also depend on how you tolerate the study drug, how your cancer responds to the study drug, and your overall condition. If you are able to tolerate the study drug and it is treating your disease, you will remain in the study until the study drug is no longer working. Not all participants will stay in the study for the same amount of time.