Expanded Access Program for SNDX-5613

Key Inclusion Criteria: Male or female participant aged ≥30 days. Not eligible for participation in an ongoing clinical study. Participant or participant's health care proxy is able and willing to provide written informed consent and able to follow study instructions. Diagnosed with relapsed/refractory acute leukemia harboring a mixed lineage leukemia rearrangement, nucleoporin 98 rearrangement, nucleophosmin 1 mutation (or mutated) mutation or any other genetic alteration with overexpression of HOXA genes predicted to potentially respond to menin inhibitors. Adequate liver, renal, and cardiac function Adequate methods of contraception are required during childbearing age from the time of enrollment through 120 days following the last study drug dose. Barrier contraception in males and double barrier in females or other highly effective method of contraception. For participants currently being treated with SNDX-5613 in a Syndax-sponsored clinical study the following criteria must be met: In the opinion of the Investigator, participant demonstrated acceptable benefit from and tolerability of the study drug Participant is considered to be compliant with study drug and procedures Participant does not meet any criteria for study drug discontinuation Investigator and participant agree to continue study drug treatment Key Exclusion Criteria: Evidence of uncontrolled infection Pregnant or nursing women. Cardiac or gastrointestinal disease. Graft-Versus-Host Disease (GVHD): Signs or symptoms of acute or chronic GVHD >Grade 1 within 4 weeks of enrollment. All transplant patients must have been off all systemic immunosuppressive therapy for at least 1 week prior to enrollment and calcineurin inhibitors for at least 1 week, with the exception of steroids. History of or any concurrent condition, therapy, laboratory abnormality, or allergy to excipients that, in the Investigator's opinion, either may interfere with the participant's participation or results in the conclusion that it is not in the best interest of the participant to participate.