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 or 2 after discussion with medical monitor
* 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
* Previous treatment with a MAT2A inhibitor and / or PRMT inhibitor
* Systemic anti-cancer therapy or major surgery within 4 weeks prior to study entry
* Radiation therapy 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
* Currently receiving another investigational study drug.
* Known or suspected hypersensitivity to IDE397/excipients or components
