Treosulfan-Based Conditioning Regimens for Allogeneic Hematopoietic Cell Transplantation in Acute Myeloid Leukemia and Other Myeloid Malignancies

Background: Treosulfan combined with fludarabine (FluTreo) has emerged as a reduced-toxicity alternative to conventional myeloablative conditioning in allogeneic hematopoietic cell transplantation (allo-HCT) for acute myeloid leukemia (AML) and related myeloid malignancies. Purpose: This study evaluates the safety, engraftment kinetics, and long-term outcomes of the FluTreo FT14 regimen in a real-world adult cohort. Materials and Methods: We conducted a prospective cohort study of 186 consecutive adults (18–70 years) undergoing allo-HCT between January 2015 and December 2024. Eligible diagnoses included de novo or secondary AML, myelodysplastic syndrome, and myelofibrosis. All received peripheral blood stem cells from matched or mismatched unrelated donors, HLA-matched siblings, or haploidentical relatives. The FT14 protocol comprised fludarabine 150 mg/m2 over five days and treosulfan 42 g/m2 over three days, with rabbit antithymocyte globulin (5 mg/kg) for unrelated grafts. Primary endpoints were neutrophil and platelet engraftment, donor chimerism, incidence of acute and chronic graft-versus-host disease (GVHD), overall survival (OS), disease-free survival (DFS), relapse, and treatment-related mortality (TRM). Kaplan–Meier, Cox regression, and Fine and Gray models were applied. Results: Median age was 59 years; diagnoses included de novo AML (43%), secondary AML (16%), MDS (25%), and MF (16%). Neutrophil and platelet engraftment medians were 10 and 12 days, respectively. Full donor chimerism (≥99%) was achieved by day 31. Grade III conditioning-related toxicity occurred in 3.2% of cases. Five-year cumulative incidences of grade II–IV acute GVHD and moderate/severe chronic GVHD were 37.6% and 30.6%. Median follow-up was 16.3 months; relapse occurred in 25.3%. Five-year OS and DFS were 71% and 49% overall (75.8% and 59% in CR1), with TRM of 15.3%. Disease relapse and acute GVHD independently predicted inferior OS, and acute GVHD predicted TRM. Conclusions: The FluTreo FT14 regimen achieves rapid engraftment, universal high donor chimerism, low severe toxicity, and durable survival, supporting its use as a myeloablative, reduced-toxicity conditioning option in myeloid malignancies.