Abstract
Haploidentical hematopoietic cell transplantation (HCT) with post-transplantation cyclophosphamide (PTCy) graft-versus-host-disease (GVHD) prophylaxis is associated with inferior overall survival (OS) compared to HLA-matched unrelated donor (MUD) HCT with PTCy prophylaxis in patients receiving reduced-intensity conditioning (RIC). Given prognostic implications of donor age, we investigated the differences in outcomes of patients with acute myeloid leukemia (AML; n = 775) undergoing RIC-HCT with a younger MUD (age <35 years; n = 84) versus a younger haploidentical donor (age <35 years; n = 302) versus an older haploidentical donor (age ≥35 years; n = 389). The older MUD group was excluded from the analysis because of small numbers. The younger haploidentical donor group (median age, 59.5 years) was somewhat younger than the younger MUD group (median age, 66.8 years) and the older haploidentical donor group (median age, 64.7 years). More patients in the MUD group received peripheral blood grafts (82%) compared to the haploidentical donor groups (55% to 56%). In multivariate analysis, compared to the younger MUD group, the younger haploidentical donor group (hazard ratio [HR], 1.95; 95% confidence interval [CI], 1.22 to 3.12; P = .005) and the older haploidentical donor group (HR, 2.36; 95% CI, 1.50 to 3.71; P < .001) had a significantly inferior OS, and the younger haploidentical donor group (HR, 3.72; 95% CI, 1.39 to 9.93; P = .009) and older haploidentical donor group (HR, 6.91; 95% CI, 2.75 to 17.39; P < .001) had a significantly higher risk of nonrelapse mortality. The older haploidentical group had a significantly higher risk of grade II-IV acute GVHD (HR, 2.29; 95% CI, 1.38 to 3.80; P = .001) and grade III-IV acute GVHD (HR, 2.70; 95% CI, 1.09 to 6.71; P = .03). There were no significant differences across the groups in the incidence of chronic GVHD or relapse. Among adult AML patients in CR undergoing RIC-HCT with PTCy prophylaxis, a young MUD may be preferred over a young haploidentical donor.