Superior GVHD-Free, Relapse-Free Survival for Haploidentical Transplant With PTCy Than Matched Unrelated Donor for AML Patients Transplanted in Second Complete Remission: A Study From the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation.

Donor preference for acute myeloid leukemia (AML) patients transplanted in second complete remission (CR2) remains unclear, and hematopoietic cell transplantation (HCT) with post-transplant cyclophosphamide (PTCy) from a haploidentical donor (HAPLO) merits attention. Data of 3878 adult AML patients receiving a first allo-HCT in CR2 from the European Society of Blood and Marrow Transplantation registry between 2010 and 2022 were analyzed. Univariate analyses and Cox regression models were used. Results of HCTs from 803 HAPLO PTCy, 1271 matched sibling donor (MSD), and 1804 matched unrelated donor (MUD) were analyzed. A higher proportion (80.7%) of patients with European LeukemiaNet (ELN2022) intermediate-/adverse-risk cytogenetics received an allo-HCT from HAPLO PTCy than from either MUD (79.6%) or MSD (70.2%). On multivariate analysis, HAPLO PTCy grafts (hazard ratio [HR] = 0.65, 95% confidence interval [CI] 0.51-0.82; p < 0.001) were associated with a lower relapse incidence (RI) compared with MSD HCTs, although non-relapse mortality was higher (HR = 1.77, 95% CI 1.34-2.34; p < 0.001). No difference was observed with respect to leukemia-free survival and graft-versus-host disease (GVHD)-free, relapse-free survival (GRFS) for HAPLO PTCy compared to MSD grafts. Notably, HAPLO PTCy HCT was associated with significantly lower RI (HR = 0.64, 95% CI 0.48-0.82; p < 0.001), chronic GVHD (cGVHD) (HR = 0.64, 95% CI 0.51-0.81; p < 0.001) and extensive cGVHD (HR = 0.47, 95% CI 0.34-0.66; p < 0.001) incidences compared to MUD HCTs. Collectively, HAPLO PTCy HCT was associated with superior GRFS (HR = 0.81, 95% CI 0.68-0.95; p = 0.013) than MUD HCT. For AML patients in CR2, HAPLO PTCy HCT is associated with lower RI and cGVHD, leading to superior GRFS compared with MUD HCTs.