Fludarabine Plus Melphalan Versus Addition of Venetoclax to Fludarabine/Melphalan Conditioning Regimen for Allogeneic Hematopoietic Stem Cell Transplantation in AML/MDS Patients Aged > 50 Years: a Multicenter, Randomized, Phase 3 Trial

Inclusion Criteria: 1. Aged \> 50 years; 2. Confirmed as acute myeloid leukemia (AML) in remission prior to transplantation, myelodysplastic syndrome (MDS; IPSS: Intermediate-2, high; or IPSS-R: Intermediate, high, very high; or IPSS-M: moderate-high, high, and very high), or myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN) by morphology, immunology, cytogenetics and molecular biology (MICM) typing; 3. Having an eligible donor and scheduled to undergo allogeneic hematopoietic stem cell transplantation (Allo-HCT) from a related or unrelated donor; 4. Karnofsky Performance Score ≥ 70; 5. Eastern Cooperative Oncology Group (ECOG) Performance Status \< 3; 6. Expected survival time \> 12 weeks; 7. Voluntarily signing the informed consent form and being able to understand and comply with all study requirements. Exclusion Criteria: 1. Complicated with severe cardiac insufficiency with a left ventricular ejection fraction (EF) \< 60%; or complicated with severe arrhythmia, and assessed by the investigator as unable to tolerate the intensive conditioning regimen; 2. Complicated with severe pulmonary insufficiency (obstructive and/or restrictive ventilatory disorder), and assessed by the investigator as unable to tolerate the intensive conditioning regimen; 3. Complicated with severe liver function impairment, with liver function indicators (alanine aminotransferase \[ALT\], total bilirubin \[TBIL\]) exceeding 3 times the upper limit of normal (ULN); and assessed by the investigator as unable to tolerate the intensive conditioning regimen; 4. Complicated with severe renal insufficiency, with serum creatinine (Cr) exceeding 2 times the upper limit of normal (ULN); or with a 24-hour creatinine clearance rate (Ccr) \< 50 ml/min, and assessed by the investigator as unable to tolerate the intensive conditioning regimen; 5. Suffering from severe active infection prior to transplantation, and assessed by the investigator as unable to tolerate the intensive conditioning regimen; 6. Having a history of allergic reactions or severe adverse reactions to the drugs involved in the conditioning regimen, and assessed by the investigator as ineligible for enrollment; 7. Other reasons for ineligibility assessed by the investigator.