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.

This study is being conducted to evaluate the safety, tolerability, dose-limiting toxicity (DLT) and determine the maximum tolerated dose (MTD) and/or recommended dose(s) for expansion (RDE) of INCA033989 administered as a Monotherapy or in Combination With Ruxolitinib in participants with myeloproliferative neoplasms.

The main purpose of this study is to evaluate safety and efficacy, and measure how much LY4584180 gets into the bloodstream and how long it takes the body to eliminate it in patients with previously treated blood cancers. For each participant, the study could last about 9 months or possibly longer including screening.