This is a Phase 1, open-label, multicenter, dose escalation and expansion study of the safety, PK, PD, and preliminary anti-tumor activity of IDE397 as a single agent and in combination with sacituzumab govitecan (SG), in adult patients with selected advanced or metastatic MTAP-deleted advanced solid tumors who are unresponsive to standard of care therapy. IDE397 is a small molecule inhibitor of methionine adenosyltransferase 2 alpha (MAT2A).

Inclusion Criteria:

• Participant must be at least 18 years of age
• Advanced or metastatic solid tumor that has progressed on at least one prior line of treatment or is intolerant to additional effective standard therapy
• Have evidence of homozygous loss of MTAP or MTAP deletion
• Willing to undergo paired fresh biopsy (pre- and post-treatment) procedure. Exceptions may be made for feasibility and safety concerns
• Measurable disease
• ECOG performance status <= 1
• Adequate organ function
• Able to swallow and retain orally administered study treatment
• Recovery from acute effects of prior therapy
• Able to comply with contraceptive/barrier requirements

Exclusion Criteria:

• Known symptomatic brain metastases
• Known primary CNS malignancy
• Current active liver or biliary disease
• Impairment of gastrointestinal (GI) function
• Active uncontrolled infection
• Clinically significant cardiac abnormalities
• Active second malignancy or history of another malignancy in the past 2 years
• Previous treatment with a MAT2A inhibitor and / or PRMT inhibitor or sacituzumab govitecan
• Systemic anti-cancer therapy, therapeutic antibody treatment, or major surgery within 4 weeks prior to study entry
• Current radiation-related toxicity or radiation therapy within 2 weeks prior to study entry
• Small molecule anti-cancer treatment within 2 weeks prior to study entry
• Prior irradiation to >25% of the bone marrow
• Current use or anticipated need for food or drugs that are known strong CYP3A4/5 inhibitors or inducers
• Require concomitant use of proton pump inhibitor
• Currently receiving another investigational study drug.
• Known or suspected hypersensitivity to IDE397/excipients or components