RecruitingPhase 1Drug trialA Study of Rebecsinib for Patients With Relapsed/Refractory Secondary Acute Myeloid Leukemia or High Risk MyelofibrosisThe purpose of this study is to test the safest and most effective dose of a new investigational drug, rebecsinib. Participants in this study will have either Secondary Acute Myeloid Leukemia (sAML) that has either returned (relapsed) or not responded to treatment (refractory) or have higher risk Myelofibrosis (MF). Participants will receive a study drug infusion on Day 1, Day 4, Day 8 and Day 11 of each 28-day cycle for a total of 6 cycles.