Study of Sapacitabine in Acute Myeloid Leukemia (AML) or Myelodysplastic Syndromes (MDS)

Inclusion Criteria: * Newly diagnosed AML based on WHO classification (Part 1) or previously treated AML or MDS (Part 2) * Age 70 years or older for whom the treatment of choice is low-intensity therapy by investigator assessment or who has refused intensive induction therapy recommended by investigator (Part 1); age 18 years or older (Part 2) * ECOG performance status 0-2 * Adequate renal function * Adequate liver function * Able to swallow capsules * Ability to understand and willingness to sign the informed consent form Exclusion Criteria: * AML is of the sub-type of acute promyelocytic leukemia or extramedullary myeloid tumor without bone marrow involvement * Known central nervous system (CNS) involvement by leukemia * Uncontrolled intercurrent illness including * Known hypersensitivity to decitabine (Part 1) or venetoclax (Part 2) * Known to be HIV-positive