Outcomes After Matched Sibling Donor Versus Haploidentical Hematopoietic Stem Cell Transplantation With Post-Transplant Cyclophosphamide-Based GVHD Prophylaxis.

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. 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. 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: .98; P = .894), disease-free survival (HR: 1.07; P = .552), relapse incidence (P = .378), and rates of acute or chronic GvHD. However, MSD recipients demonstrated significantly earlier neutrophil engraftment (HR: 1.20; P = .036) and a nonsignificant trend toward lower nonrelapse mortality (HR: .70; P = .055). 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.