Outcomes of mixed phenotype acute leukemia undergoing allogeneic stem cell transplantation: a retrospective study of the ALWP of EBMT.

Limited data is available on outcomes of mixed phenotype acute leukemia (MPAL) following allogeneic stem cell transplantation (HCT), and the impact of haploidentical HCT with post-transplant cyclophosphamide in this setting is lacking. We retrospectively analyzed 195 adults with MPAL undergoing HCT in first complete remission from 2014 to 2023. The 2-year overall survival (OS) and leukemia free survival (LFS) were 70.7% and 56.4%. Relapse incidence (RI) was 29.8% and non-relapse mortality was 13.8% at 2 years. The cumulative incidence of grade II-IV and III-IV acute graft versus host disease (GvHD) was 28.8% and 9.3% at 100 days. The 2-year cumulative incidence of chronic GvHD was 36.6%. The 2-year GvHD-free-relapse free survival was 37.6% (95%CI 29.9-45.3%). In multivariate analysis, patients undergoing myeloablative conditioning had better OS (HR 0.5, 95%CI 0.27-0.93, p = 0.03) and LFS (HR 0.49, 95%CI 0.26-0.94, p = 0.03). The use of peripheral blood was associated with better LFS (HR 0.36, 95%CI 0.17-0.76, p = 0.008) and lower RI (HR 0.33, 95%CI 0.12-0.93, p = 0.04). In vivo T-cell depletion was associated with lower incidence of chronic GvHD (HR 0.32, 95%CI 0.17-0.63, p < 0.001). These findings highlight that conditioning intensity, graft source, and T-cell depletion strategies are critical factors in optimizing transplant outcomes for MPAL.