Comparative study of treosulfan plus Fludarabine (FT14) with busulfan plus Fludarabine (FB4) for acute myeloid leukemia in first or second complete remission: An analysis from the European Society for Blood and Marrow Transplantation (EBMT) Acute Leukemia Working Party (ALWP).

Different doses of treosulfan plus fludarabine have shown advantage over reduced intensity regimens. However, data comparing higher doses of treosulfan to myeloablative busulfan are limited. Thus, we compared outcomes between FT14 (fludarabine 150/160 mg/m 2 and treosulfan 42 g/m 2 , or FT14) over FB4 (fludarabine 150/160 mg/m 2 and busulfan 12.8 mg/kg). We retrospectively studied patients from European Society for Blood and Marrow Transplantation registry: a) adults diagnosed with acute myeloid leukemia (AML), b) recipients of first allogeneic hematopoietic stem cell transplantation (HSCT) from unrelated or sibling donor (2010-2020), c) HSCT at first or second complete remission, d) conditioning with FT14 or FB4. FT14 recipients (n = 678) were older, with higher rates of secondary AML, unrelated donors, peripheral blood grafts, and adverse cytogenetics, but lower percentage of female donor to male recipient compared to FB4 (n = 2025). Analysis was stratified on age. In patients aged < 55 years, FT14 was associated with higher relapse incidence (RI) and lower Leukemia-Free Survival (LFS). In patients aged≥55 years, acute GVHD CI was higher in FB4, without significant differences in other outcomes. Although FT14 has been used for higher-risk HSCT patients, our large real-world multicenter study suggests that FB4 is associated with better outcomes compared to FT14 in younger patients.