Treosulfan or busulfan plus clofarabine as reduced intensity conditioning regimen before allotransplant for adults with myeloid malignancies.

This single-center retrospective study included 142 adults with myeloid malignancies undergoing allogeneic hematopoietic stem cell transplantation with peripheral blood stem cells from matched related or unrelated donors between 2010 and 2023. The aim was to compare outcomes between patients receiving a clofarabine-based reduced-intensity conditioning regimen combined either with busulfan (CloB2, n = 108) or treosulfan (CloT3, n = 34). CloB2 consisted of busulfan 3.2 mg/kg/day 2 days (d) with 1 or 2 d of anti-thymocyte globulin (ATG). CloT3 consisted of treosulfan 10 g/m²/d 3 d and 2 d of ATG. The CloT3 group included more patients with adverse-risk acute myeloid leukemia (AML). Neutrophil recovery was significantly faster after CloT3, resulting in a shorter hospital stay. No significant differences were observed between groups regarding overall survival (OS), disease-free survival (DFS) and graft-versus-host disease (GVHD)-free/relapse-free survival, non-relapse mortality (NRM), relapse incidence (RI), or acute and chronic GVHD. Among AML patients, univariable analysis showed similar outcomes, except for slower neutrophil recovery and higher RI with CloB2. In multivariable analysis, adverse ELN-2017 risk score, was associated with lower OS and DFS. CloT3 was independently associated with improved OS (p = 0.038), DFS (p = 0.026) and lower RI (p = 0.024). These exploratory results support further prospective studies, particularly in AML patients.