Study of Revumenib, Azacitidine, and Venetoclax in Pediatric and Young Adult Patients With Refractory or Relapsed Acute Myeloid Leukemia

This is a research study to find out if adding a new study drug called revumenib to commonly used chemotherapy drugs is safe and if they have beneficial effects in treating patients with acute myeloid leukemia (AML) or acute leukemia of ambiguous lineage (ALAL) that did not go into remission after treatment (refractory) or has come back after treatment (relapsed), and to determine the total dose of the 3-drug combination of revumenib, azacitidine and venetoclax that can be given safely in participants also taking an anti-fungal drug. Primary Objective * To determine the safety and tolerability of revumenib + azacitidine + venetoclax in pediatric patients with relapsed or refractory AML or ALAL. Secondary Objectives * Describe the rates of complete remission (CR), complete remission with incomplete count recovery (CRi), and overall survival for patients treated with revumenib + azacitidine + venetoclax at the recommended phase 2 dose (RP2D).

Inclusion Criteria: Participants must have a diagnosis of AML or ALAL and meet the criteria below: * Refractory leukemia, defined as persistent leukemia after at least two courses of induction chemotherapy (one course for secondary AML), or relapsed leukemia, defined as the re-appearance of leukemia after the achievement of remission. Patients must have ≥5% blasts in the bone marrow as assessed by morphology or ≥1% blasts flow cytometry. However, if an adequate bone marrow sample cannot be obtained (e.g., in a patient with acute megakaryoblastic leukemia with marrow fibrosis), patients may be enrolled if there is unequivocal evidence of leukemia with ≥5% blasts by morphology or ≥1% blasts flow cytometry in the blood. * Presence of KMT2A rearrangement (KMT2Ar), NUP98 rearrangement (NUP98r), NPM1 mutation or fusion, PICALM::MLLT10, DEK::NUP214, UBTF-TD, KAT6A rearrangement (KAT6Ar), or SET::NUP214 * Adequate organ function, defined as total bilirubin \< 1.5 × institutional upper limit of normal for age or normal conjugated bilirubin (for patients with known Gilbert's syndrome, total bilirubin \ 16 years old. * At least 14 days or 5 half-lives (whichever is longer) must have elapsed since the completion of myelosuppressive therapy, with the exception of low-dose therapy used for cytoreduction according to institutional standards, such as hydroxyurea or low-dose cytarabine (up to 200 mg/m\^2/day). In addition, all toxicities must have resolved to grade 1 or less. * Patients must have a leukocyte count \