Azacitidine, Venetoclax, and Gilteritinib in Treating Patients With Recurrent/Refractory FLT3-Mutated Acute Myeloid Leukemia, Chronic Myelomonocytic Leukemia, or High-Risk Myelodysplastic Syndrome/Myeloproliferative Neoplasm

PRIMARY OBJECTIVES: I. To establish the maximum tolerated dose (MTD) of the combination of azacitidine, venetoclax and gilteritinib in patients with relapsed/refractory FLT3-mutated acute myeloid leukemia (AML) or chronic myelomonocytic leukemia (CMML) or high-risk myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN). (Phase I) II. To determine the complete remission/complete remission with incomplete count recovery (CR/CRi) rate of the regimen in patients with newly diagnosed or relapsed/refractory fms-like tyrosine kinase 3 (FLT3)-mutated AML or CMML or high-risk MDS/MPN. (Phase II) SECONDARY OBJECTIVES: I. To assess other efficacy endpoints (CR rate, minimal residual disease negativity by flow cytometry, relapse-free survival, overall survival). II. To assess proportion of patients proceeding to hematopoietic stem cell transplantation (HSCT). III. To determine the safety of the combination regimen. EXPLORATORY OBJECTIVES: I. To evaluate the impact of baseline genomic alterations on response and survival of the combination regimen. II. To determine the impact of baseline FLT3 allelic ratio on response and survival. III. To evaluate clonal evolution from diagnosis to relapse using single-cell sequencing. OUTLINE: This is phase I, dose-escalation study of gilteritinib followed by a phase II study. Patients receive azacitidine subcutaneously (SC) or intravenously (IV) over 30-60 minutes on days 1-7, venetoclax orally (PO) once daily (QD) on days 1-28 of cycle 1 and on days 1-21 of subsequent cycles, and gilteritinib PO QD on days 1-28. Treatment of azacytidine and venetoclax repeats every 28 days for up to 24 cycles in the absence of disease progression or unacceptable toxicity. Cycles of gilteritinib repeat every 28 days in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up at 30 days and then every 6 months thereafter.