Fludarabine, busulfan, and melphalan conditioning regimen in allogeneic hematopoietic stem cell transplantation for adult patients with myeloid malignancies: A multicenter retrospective study.

Relapse remains the main cause of treatment failure in patients with myeloid malignancies even after allogeneic hematopoietic stem cell transplantation (allo-HSCT). We observed a particularly low incidence of relapse in patients prepared with fludarabine, busulfan and melphalan in our previous study and this multicenter retrospective analysis aimed to confirm the feasibility of the regimen and to identify the potential prognostic factors. This study was performed using registry data from adults patients with myeloid malignancies who underwent their first allo-HSCT following fludarabine(≥100 mg/m 2 ), busulfan (≥3.2 mg/kg) and melphalan (≥100 mg/m 2 ) based conditioning at nine transplantation centers in China between Jan. 2020 and Mar. 2022. A total of 221 consecutive patients (AML n  = 171, MDS-IB-1 or 2 n  = 44, CMML n  = 6) with median age of 46 were enrolled in this study. The median follow-up was 507 days for survivors. The 2-year NRM, CIR, OS and DFS were 10.6% ± 2.2%, 14.8% ± 3.3%, 79.4% ± 3.7% and 74.6% ± 3.7%, respectively. In multivariate analyses, high HCT-CI (≥3) was the only independent factor for higher NRM [hazard ratio (HR), 2.96; 95% confidence interval (CI), 1.11 to 7.90; p  = 0.030] and ECOG score ≥2 was the only independent factor for inferior OS (HR, 2.43; 95%CI, 1.15 to 5.16; p  = 0.020) and DFS (HR, 2.12; 95%CI, 1.13 to 4.02; p  = 0.020). AML diagnosis and positive measurable residual disease (MRD) at transplantation were predictors for higher CIR (HR = 7.92, 95%CI 1.05-60.03, p  = 0.045; HR = 3.64, 95%CI 1.40-9.44, p  = 0.008; respectively), while post-transplantation cyclophosphamide based graft-versus-host disease prophylaxis was associated with lower CIR (HR = 0.24 95%CI 0.11-0.54, p  = 0.001). The intensity of conditioning regimen did not impact CIR, NRM, DFS and OS. These results supported that double alkylating agents of busulfan and melphalan based conditioning regimens were associated with low relapse rate and acceptable NRM in adult patients with myeloid malignancies. The optimal dose remained to be confirmed by further prospective studies.