A Phase 1a/1b Study of the Safety, Pharmacokinetics, and Antitumor Activity of the Oral Menin Inhibitor Ziftomenib in Combination With Imatinib in Patients With Advanced Gastrointestinal Stromal Tumors (GIST) After Imatinib Failure

Key Inclusion Criteria:

• Documented diagnosis of advanced or metastatic KIT mutant GIST.
• Documented disease progression on imatinib therapy as current or prior treatment.
• Eastern Cooperative Oncology Group (ECOG) performance status (PS) of ≤2 at screening.
• At least 1 measurable lesion per mRECIST.
• Negative pregnancy test for female patients of childbearing potential.
• Adequate organ function per protocol requirements.
• Resolution of all clinically significant toxicities from prior therapy to ≤Grade 1 (or patient baseline) within 1 week prior to the first dose of study drug.
• Participant, or legally authorized representative, must be able to understand and provide written informed consent prior to the first screening procedure.

Key Exclusion Criteria:

• Diagnosis of non-KIT mutation or a T670X KIT mutation-driven GIST.
• History of prior or currently has cancer which 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 prior to 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 prior to the first dose of study intervention.
• Is pregnant or lactating.
• Gastrointestinal abnormalities that may impact taking study intervention by mouth.
• Actively bleeding, excluding hemorrhoidal or gum bleeding.