Matched unrelated vs haploidentical donor hematopoietic cell transplantation using posttransplant cyclophosphamide.

Posttransplant cyclophosphamide (PTCy)-based graft-versus-host disease (GVHD) prophylaxis is now standard for matched unrelated donor (MUD) hematopoietic cell transplantation (HCT). Previous studies comparing MUD and haploidentical donor HCT using PTCy were limited in size and follow-up. We therefore performed a registry-based analysis examining the impact of donor type on HCT with PTCy. Adult patients (n = 5873) receiving MUD (n = 1973) or haploidentical (n = 3900) HCT with PTCy for acute leukemia (74.2%) or myelodysplastic syndrome (MDS; 25.8%) reported to the Center for International Blood and Marrow Transplant Research between 2017 and 2021 were included. Primary end points were 3-year overall survival (OS) and GVHD-free, relapse-free survival (GRFS). Cox regression and sensitivity analyses were performed through adjustment of propensity scores. Haploidentical HCT had worse OS (hazard ratio [HR], 1.15; 95% confidence interval [CI], 1.04-1.27; P = .005) and GRFS (HR, 1.19; 95% CI, 1.10-1.29; P < .001) versus MUD HCT. Donor age was the only other donor factor associated with survival. Results were confirmed in sensitivity analysis. When restricted to reduced intensity conditioning or donors <30 years, OS did not differ between groups. Haploidentical HCT was associated with higher primary graft failure (HR, 1.67; P = .002), increased grade 3/4 acute GVHD (HR, 1.28; P = .039), higher moderate/severe chronic GVHD (HR, 1.47; P < .001), and nonrelapse mortality (HR, 1.34; P < .001). Grade 2 to 4 acute GVHD and relapse risk did not differ. This large analysis showed that in adults with acute leukemia or MDS, MUD HCT was associated with improved outcomes versus haploidentical HCT with PTCy-based GVHD prophylaxis.