Eltanexor and Venetoclax in Relapsed or Refractory Myelodysplastic Syndrome and Acute Myeloid Leukemia

This phase I trial tests the safety, side effects, and best dose of eltanexor in combination with venetoclax for the treatment of patients with myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) that has come back after a period of improvement (relapsed) or that has not responded to previous treatment (refractory). Eltanexor works by trapping "tumor suppressing proteins" within the cell, thus causing the cancer cells to die or stop growing. Venetoclax is in a class of medications called B-cell lymphoma-2 (BCL-2) inhibitors. It may stop the growth of cancer cells by blocking Bcl-2, a protein needed for cancer cell survival. Giving eltanexor together with venetoclax may be safe, tolerable and/or effective in treating patients with relapsed or refractory MDS or AML.

Inclusion Criteria: \- Age \>/= 18 years at the time of signing the Informed Consent Form (ICF); must voluntarily sign an ICF; and must be able to meet all study requirements. For Myelodysplastic Syndrome (MDS): Morphologically confirmed diagnosis of MDS with increased blasts (\>/= 5%), with a prior DNA methyltransferase inhibitor (DNMTi) treatment and progression after 2 cycles or stable disease after 4 cycles For Acute Myeloid Leukemia (AML): Morphologically confirmed diagnosis of AML in accordance with WHO diagnostic criteria that is relapsed or refractory following \>/= 1 line(s) of therapy. * WBC must be less than 25,000/ul prior to study start (hydroxyurea allowed). * A bone marrow aspirate must be performed, and tissue collected for entrance to the trial unless circulating blasts \>/= 5% in which case, peripheral blood can be used. * Eastern Cooperative Oncology Group Performance Status of 0 - 2. * Must have adequate hepatic and renal function as demonstrated by the following: ALT(SGPT) and/or AST (SGOT) \