Comparison of Nonrelapse Mortality After Haploidentical Hematopoietic Stem Cell Transplantation With Post-transplant Cyclophosphamide Versus Single Umbilical Cord Blood Transplantation in Hematologic Disease

•UCBT with high CD34+ cell counts offered similar NRM and OS to PTCy-haplo.•UCBT with low CD34+ cell counts showed worse NRM and OS to PTCy-haplo.•High NRM in UCB-low was attributed to high infection-related mortality. Unrelated cord blood transplantation (UCBT) and haploidentical transplantation using posttransplant cyclophosphamide (PTCy-haplo) are alternatives for patients lacking a human leukocyte antigen-matched donor. CD34+ cell counts in cord blood affect transplantation outcomes, particularly nonrelapse mortality (NRM). The primary objective of this study was to compare the transplantation outcomes after UCBT and PTCy-haplo focusing on CD34+ cell counts in cord blood. This retrospective study used data from 2014 to 2020 from a Japanese nationwide database. UCBT cases were divided into those with UCBT with higher (UCB-H; ≥.84 × 105/kg) and lower (UCB-L;