Comparison of clinical outcomes between early and delayed allogeneic hematopoietic stem cell transplantation for severe aplastic anemia: a single-center retrospective study.

Allogeneic hematopoietic stem-cell transplantation (allo-HSCT) is the only curative therapy for severe aplastic anemia (SAA), yet the prognostic impact of the diagnostic-to-transplant interval on first allo-HSCT remains contentious. To determine whether a waiting time > 1 year from diagnosis to first allo-HSCT compromises engraftment, virus reactivation, GVHD, OS and GRFS in SAA. A single-center retrospective cohort study of 255 consecutive SAA patients receiving their first allo-HSCT between 2018 and 2025. After 1:2 propensity-score matching (caliiper 0.2), patients were stratified into Early (≤ 1 year, n = 170) and Delayed (> 1 year, n = 85) groups. Baseline characteristics were well balanced. The Early group exhibited a significantly lower CMV reactivation rate (24.1% vs. 40.0%, P = 0.008). No significant differences were observed in grade II-IV aGVHD, cGVHD, 5-year OS or GRFS. Subgroup analyses demonstrated superior survival among patients aged ≤ 40 years, those with MSD donors and received FABT-based regimen. Early allo-HSCT improves transplant outcomes in SAA by reducing CMV reactivation, especially in very severe cases. Eligible patients should be referred promptly and transplanted without delay.