Has early mortality following single-unit unrelated cord blood transplantation improved in recent years? A nationwide registry data analysis from 2003 to 2022 in Japan.

Unrelated single-unit cord blood transplantation (CBT) is a valuable alternative donor source for patients without matched related or unrelated donors. Although initial concerns included limited cell dose, delayed haematopoietic recovery and higher early mortality, advancements in transplant practices may have led to improved outcomes. However, it remains uncertain whether these improvements extend to the most recent years. We conducted a nationwide, registry-based retrospective study of 15 816 patients who received unrelated single-unit CBT in Japan and analysed across four time periods: 2003-2007, 2008-2012, 2013-2017 and 2018-2022. Overall survival (OS) improved significantly across time periods, with 3-year OS increasing from 38.8% (2003-2007) to 54.4% (2018-2022; p < 0.001). Similarly, 100-day non-relapse mortality declined from 19.6% to 9.5% (p < 0.001). Neutrophil and platelet engraftment rates also rose steadily, reaching 89.6% and 78.0%, respectively, in the most recent period. The most notable improvement in 100-day OS occurred among patients aged ≥60 years. Early mortality within 100 days due to bacterial and fungal infections, graft failure, haemorrhage and graft-versus-host disease (GVHD) significantly decreased over time. This study shows clear and consistent improvements in transplant outcomes, especially in the most recent 5-year period.