Allo-SCT for AML and MDS with treosulfan compared with BU-based regimens: reduced toxicity vs reduced intensity. 
Allo-SCT with reduced-intensity conditioning (RIC) results in lower non-relapse mortality (NRM), but higher relapse rate than myeloablative conditioning (MAC) in AML/myelodysplastic syndromes (MDS).  Novel regimens with intensive anti-leukemic activity, but with limited toxicity will be of benefit.  In all, 85 patients with AML/MDS, not eligible for MAC, were given fludarabine-treosulfan conditioning (FT).  Outcomes were compared with those in patients given fludarabine-BU RIC (FB2, n=106) or reduced-toxicity (RTC) conditioning (FB4, fludarabine and myeloablative BU dose, n=85).  The 5-year NRM was 29%, 20% and 18% after FT, FB2 and FB4, respectively (P=NS).  Multivariate analysis (MVA) identified comorbidity score (HCT-CI) >2 and advanced disease as adverse factors with no independent impact of regimen.  The 5-year relapse rate was 36%, 47% and 40%, respectively (P=0.17).  MVA identified advanced disease as the major adverse factor, while FT had significantly lower relapse rate (hazard ratio 0.6, P=0.03).  The 5-year survival (OS) was 37% with advanced disease.  HCT-CI >2 and age ≥ 50 were found as adverse factors.  The 5-year OS was 46%, 44% and 50% after FT, FB2 and FB4 in early-intermediate-stage disease (P=NS) and 33%, 9% and 28% in advanced disease, respectively (P=0.02).  FT is an RTC regimen with intensive anti-leukemia effect in MAC non-eligible patients.