Unrelated or haploidentical allogeneic hematopoietic cell transplantation in second complete remission for acute myeloid leukemia—Improved outcomes over time: A European Society for Blood and Marrow Transplantation Acute Leukemia Working Party study

Background: Allogeneic hematopoietic cell transplantation (allo‐HCT) is the only cure for acute myeloid leukemia (AML) in second complete remission (CR2). Patients lacking a matched sibling donor (MSD) receive transplants from matched unrelated donors (MUDs), mismatched unrelated donors (MMUDs), haploidentical (haplo) donors, or cord blood. Methods: This is a retrospective, registry‐based European Society for Blood and Marrow Transplantation study that investigates changes in patient‐ and transplant‐related characteristics and posttransplant outcomes over time. Results: We identified 3955 adult patients (46.7% female; median age, 52 years [range, 18–78 years]) with AML in CR2 first transplanted between 2005 and 2019 from a MUD 10/10 (61.4%), MMUD 9/10 (21.9%), or haplo donor (16.7%) and followed for 3.7 years. A total of 725 patients were transplanted between 2005 and 2009, 1600 between 2010 and 2014, and 1630 between 2015 and 2019. Over the three time periods, there was a significant increase in patient age (from 48.7 to 53.5 years; p <.001), use of a haplo donor (from 4.6% to 26.4%; p <.001), and use of posttransplant cyclophosphamide (from 0.4% to 29%; p <.001). There was a significant decrease in total body irradiation and in vivo T‐cell depletion. In multivariate analysis, transplants performed more recently had better outcomes. Leukemia‐free survival (hazard ratio [HR], 0.79; p =.002) and overall survival (HR, 0.73; p <.001) increased over time. Similarly, nonrelapse mortality (HR, 0.64; p <.001) decreased over time. We also observed better graft‐vs‐host disease (GVHD) rates (acute GVHD II–IV: HR, 0.78; p =.03; GVHD‐free, relapse‐free survival: HR, 0.69; p <.001). Conclusions: Even in the absence of an MSD, outcomes of allo‐HCT in CR2 for AML have significantly improved over time, with most favorable outcomes achieved with a MUD. Allogeneic transplantation remains the only curative option for patients with acute myeloid leukemia in second complete remission, with significant changes in patient and transplant characteristics and posttransplant outcomes over time. Even in the absence of matched sibling donors, outcomes have improved over time, with the best outcomes achieved with matched unrelated donors. [ABSTRACT FROM AUTHOR]