Study of Venetoclax and Azacitidine in Advanced BCR-ABL Negative Myeloproliferative Neoplasms

Inclusion Criteria: * Ability to voluntarily provide written informed consent. * Documented diagnosis per World Health Organization (WHO) 2016 criteria of BCR-ABL negative myeloproliferative neoplasms (MPN). * Documented MPN transformation to accelerated phase (AP) or blast phase (BP) without prior blast reduction therapy for their AP/BP disease. * Eastern Cooperative Oncology Group (ECOG) performance status 0-2. * Adequate organ function. * Must practice at least one reliable method of birth-control starting at least on cycle 1 day 1 until at least 90 days after the last dose of study drug. * Female participants of childbearing potential must have a negative serum pregnancy test within 14 days prior to cycle 1 day 1. Exclusion Criteria: * History of allogeneic stem cell transplant for MPN. * Previous treatment with venetoclax, navitoclax, azacytidine or other hypomethylating agents (HMA). * White blood cell count \>25 x 10\^9/L. * Current enrollment in another interventional study. * Presence of any active uncontrolled infection such as bacterial or fungal infections progressing despite adequate antimicrobial treatment. * Myocardial infarction in the preceding 3 months. * Active human immunodeficiency virus (HIV), hepatitis B (HBV), hepatitis C (HCV) infection. * History of active malignancy in the previous 2 years. * Any psychiatric illness or social circumstances or significant co-morbid conditions that may compromise study participation. * Pregnant or breastfeeding women. * Patients with known central nervous system (CNS) involvement with acute myeloid leukemia (AML) or CNS extramedullary hematopoiesis. * Patients with t (15;17) * Patients who have received strong and/or moderate CYP3A inducers within 7 days prior to the initiation of study treatment. * Active COVID-19 infection. * History of prior blast-reduction therapy for AP/BP-MPN. * Preceding history MDS, chronic myelomonocytic leukemia (CMML), and other myelodysplastic syndromes (MDS)/MPN overlap syndromes.