Abstract
Relapse remains the leading cause of treatment failure after allogeneic hematopoietic stem cell transplantation for acute myeloid leukemia and myelodysplastic syndromes. Post-transplant treatment may provide a third anti-leukemic effect after conditioning-related cytotoxicity has waned and before graft-versus-leukemia immunity is fully established. Prophylactic maintenance is initiated in high-risk patients despite undetectable measurable residual disease (MRD), whereas pre-emptive treatment is triggered by the detection of MRD or declining donor chimerism. Hypomethylating agents (HMAs) are biologically attractive and feasible with post-transplant-adapted dosing, but prophylactic azacitidine did not improve relapse-free or overall survival in a randomized trial. Newer decitabine-based, oral HMA, and venetoclax-containing strategies require confirmation. FMS-like tyrosine kinase 3 (FLT3) inhibitors have the strongest prospective evidence in a molecularly selected population. The QuANTUM-First trial supports quizartinib throughout induction, consolidation, and continuation, including after transplantation, whereas the MORPHO trial directly evaluated post-transplant gilteritinib and identified its clearest benefit in patients with detectable peri-transplant FLT3-internal tandem duplication (FLT3-ITD) MRD. This review traces the evolution of relapse prevention strategies and proposes a practical framework integrating baseline risk, serial MRD assessment, targetable biology, immune intervention, and post-transplant feasibility.