A Study of Ziftomenib in Combination With Imatinib in Patients With Advanced Gastrointestinal Stromal Tumors (GIST)

Key Inclusion Criteria:

* Documented diagnosis of advanced/metastatic KIT-mutant GIST.
* Documented disease progression on imatinib as current or prior therapy.
* Eastern Cooperative Oncology Group (ECOG) performance status of ≤2 at screening.
* At least 1 measurable lesion per RECIST v1.1 modified for GIST.
* Negative pregnancy test for participants of childbearing potential.
* Adequate organ function per protocol requirements.
* Resolution of all clinically significant toxicities from prior therapy to \<Grade 1 (or participant baseline) within 1 week before the first dose of study intervention.
* Participant, or legally authorized representative, must be able to understand and provide written informed consent before the first screening procedure.

Key Exclusion Criteria:

* Diagnosis of GIST without a KIT mutation or with a T670X KIT mutation.
* History of prior or current cancer that has potential to interfere with obtaining study results.
* Received a prohibited medication, including investigational therapy, less than 14 days or within 5 drug half-lives before the first dose of study intervention.
* Active central nervous system metastases.
* Uncontrolled intercurrent illness, including, but not limited to protocol defined cardiac disease.
* Mean corrected QT interval (QTcF) greater than 470ms.
* Left ventricular ejection fraction (LVEF) \<50%.
* Major surgery within 2 weeks before the first dose of study intervention.
* Is pregnant or breastfeeding.
* Gastrointestinal abnormalities that may impact taking study intervention by mouth.
* Actively bleeding, excluding hemorrhoidal or gum bleeding.