[Prophylactic or Pre-Emptive Therapy with Azacitidine or FLT3 Inhibitor after Allogeneic Hematopoietic Stem Cell Transplantation for AML and MDS].

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an established curative treatment for acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Advances in supportive care, infection control, and graft-versus-host disease management have substantially reduced non-relapse mortality, leading to improved transplant outcomes. However, post-transplant relapse remains the leading cause of treatment failure, particularly in patients with adverse genetic abnormalities or active disease at transplantation. Post-transplant maintenance therapy has emerged as a strategy to prevent relapse by providing a "third anti-leukemic effect" that complements the cytotoxic effect of conditioning regimens and the graft-versus-leukemia immune response. Maintenance approaches can be broadly categorized into prophylactic therapy administered during molecular remission and preemptive therapy initiated upon detection of measurable residual disease (MRD). This review summarizes the current concepts of post-transplant maintenance therapy in AML/MDS, with a particular focus on hypomethylating agents such as azacitidine and FLT3 inhibitors. It also discusses emerging evidence supporting MRD-guided treatment strategies and molecularly targeted maintenance approaches, highlighting future perspectives for optimizing relapse prevention after allo-HSCT.