A new study has reported that a conditioning regimen with fludarabine and a myeloablative dose of busulfan (FB4) may offer patients 55 years of age or older with myelodysplastic syndromes (MDS) prolonged remission.

The study, published in Transplantation and Cellular Therapies, noted that the relapse rate in this patient group was similar to that of previous studies.

“Recent efforts to identify new approaches to reduce transplant-related mortality include the use of novel conditioning regimens that are less toxic than traditional myeloablative conditioning and reduced-intensity conditioning regimens,” the authors wrote. “Herein we report the outcome of acute myeloid leukemia and MDS patients who were transplanted following myeloablative conditioning with fludarabine and single daily administration of intravenous busulfan, stratified according to hematopoietic stem cell transplant comorbidity index (HCT-CI) score and age.”

The research team conducted a retrospective study of the outcomes of 103 patients with acute myeloid leukemia or MDS with excess of blasts who underwent FB4 conditioning prior to allogeneic hematopoietic stem cell transplants between May 2015 and November 2020 at a single center in London.

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The primary outcome was overall survival, and secondary outcomes were total overall survival, transplant-related mortality, graft versus host disease (GVHD), and GVHD-relapse free survival.

The results showed that 2- and 5-year total overall survival (OS) was 62% and 53%, respectively, with patients aged 55 years and over achieving an overall survival of 51% and 44%, respectively. The cumulative incidence of transplant-related mortality was 26%.

GVHD and GVHD-relapse free survival were encouraging, given that patients 55 year of age or older without significant comorbidities (HCT-CI score <2) achieved a 2-year GVHD-relapse free survival of 51% compared with only 19% in patients with HCT-CI scores of 2 or more.

The authors conclude that the FB4 conditioning regimen generally offers prolonged remission with acceptable safety, and it can be considered for patients aged 55 years or more in the absence of significant comorbidities.  


Avenoso D, Mehra V, Slonim LB, et al. Myeloablative dose of busulfan and fludarabine combined with in vivo T-cell depletion is a safe and effective conditioning for acute myeloid leukaemia and myelodysplastic syndrome patients. Transplant Cell Ther. Published online August 12, 2023. doi:10.1016/j.jtct.2023.08.12