Outcomes after Matched Sibling Donor versus Haploidentical Hematopoietic Stem Cell Transplantation with Post-Transplant Cyclophosphamide-Based GVHD Prophylaxis.

BACKGROUND: Outcomes of allogeneic hematopoietic stem cell transplantation (allo-HSCT) are heavily influenced by donor type. While matched sibling donors (MSD) have traditionally been the preferred source, the use of haploidentical (haplo) donors has expanded following the introduction of post-transplant cyclophosphamide (PTCy). This study compares clinical outcomes between MSD and haplo-HSCT recipients treated with uniform PTCy-based prophylaxis. METHODS: In this retrospective multicenter study utilizing the CIBMTR registry, we analyzed 875 adult patients with acute myeloid leukemia, acute lymphoblastic leukemia, or myelodysplastic syndromes who underwent their first allo-HSCT between 2012 and 2017. Outcomes, including survival, relapse, and graft-versus-host disease (GvHD), were modeled using Cox proportional hazards regression to report hazard ratios (HR) with 95% confidence intervals. RESULTS: The cohort comprised 558 (63.8%) haplo-HSCT and 317 (36.2%) MSD-HSCT recipients. Multivariable analyses indicated that MSD-HSCT was associated with outcomes comparable to haplo-HSCT for overall survival (HR: 0.98; p=0.894), disease-free survival (HR: 1.07; p=0.552), relapse incidence (p=0.378), and rates of acute or chronic GvHD. However, MSD recipients demonstrated significantly earlier neutrophil engraftment (HR: 1.20; p=0.036) and a non-significant trend toward lower non-relapse mortality (HR: 0.70; p=0.055). CONCLUSION: Haplo-HSCT using PTCy demonstrates efficacy comparable to MSD-HSCT across major transplant endpoints, including survival and relapse. While minor differences in engraftment kinetics exist, these findings support the wider adoption of haploidentical donors with PTCy as a robust therapeutic alternative for patients lacking a matched sibling donor.