A randomized phase III study of pretransplant conditioning for AML/MDS with fludarabine and once daily IV busulfan ± clofarabine in allogeneic stem cell transplantation

Pretransplant conditioning with Fludarabine (Flu)-Busulfan (Bu) is safe, but clofarabine (Clo) has improved antileukemic activity. Hypothesis: Flu+Clo-Bu (FCB) yields superior progression-free survival (PFS) after allogeneic transplantation. We randomized 250 AML/MDS patients aged 3-70, Karnofsky Score >= 80, with matched donors, to FCB (n = 120) or Flu-Bu (n = 130), stratifying complete remission (CR) vs. No CR, (NCR). HCT-CI scores varied, from 0 to 10. All evaluable patients engrafted. Median follow-up was 66 months (interquartile range: 58-80). Three-year relapse incidence (RI), 25% with FCB, vs. 39% with Flu-Bu (p = 0.018), offset by higher non-relapse mortality, 22.6% (95%CI: 16-30.2%) vs. 12.3% (95%CI: 6.5-19%). Three-year PFS was 52% (95%CI: 44-62%) (FCB), vs. 48% (95%CI: 41-58%) (Flu-Bu). FCB benefited CR patients less, NCR patients age <= 60 had 3-year 34% RI (95%CI: 19-49%) (FCB) vs. 56% (95%CI: 38-70%) after Flu-Bu (p = 0.037). NCR patients >60 years had 3-year RI 10.0% (FCB), vs. 56.0%, after Flu-Bu (p = 0.003). Bayesian regression analysis including treatment-covariate interactions showed FCB superiority in NCR patients with low HCT-CI (0-2). Serious adverse event profiles were similar for the regimens. Conditioning with FCB did not improve PFS overall, but improved disease control in NCR patients, mandating confirmatory trials. Remission status and HCT-CI should be considered when using FCB.

Automated summary

Pretransplant conditioning with Fludarabine-Busulfan is safe, but clofarabine has improved antileukemic activity. This study aimed to evaluate the efficacy of Flu+Clo-Bu (FCB) compared to Flu-Bu in AML/MDS patients undergoing allogeneic transplantation. The results showed that FCB had a lower relapse incidence but higher non-relapse mortality compared to Flu-Bu. FCB showed improved disease control in NCR patients with low HCT-CI scores. Confirmatory trials are needed to further assess the effectiveness of FCB.