Comparable outcomes for pediatric acute lymphoblastic leukemia patients receiving conditioning with total body irradiation or chemotherapy: A nationwide, Korean registry-based study.

Acute lymphoblastic leukemia (ALL) is the predominant malignancy in pediatric patients, and allogeneic hematopoietic stem cell transplantation (HSCT) plays a critical role in high-risk cases. However, real-world nationwide data comparing the outcomes of conditioning regimens are limited. This nationwide registry-based study analyzed data from 270 Korean pediatric patients with high-risk or relapsed ALL who underwent their first allogeneic HSCT with myeloablative conditioning. Among all analyzed patients, 118 received total body irradiation-based conditioning (MAC-TBI) and 152 received chemotherapy-based conditioning (MAC-Chemotherapy), of whom 96.6% underwent busulfan-based regimens. MAC-TBI recipients were older at diagnosis and at HSCT. No significant differences were observed between groups in neutrophil or platelet engraftment times, or infused CD34+ cell doses. Acute graft-versus-host disease (GVHD) incidences (grades II-IV and III-IV) were comparable, although chronic GVHD incidence tended to be lower in the MAC-Chemotherapy group (21.0% vs. 31.1%, P = 0.072). Additionally, the 5-year event-free survival (EFS) rates for MAC-TBI versus MAC-Chemotherapy were 73.7% and 69.8% (P = 0.827), respectively; the 5-year overall survival (OS) rates were 76.3% and 80.2% (P = 0.941), respectively, indicating that conditioning regimen did not significantly impact survival. Pediatric disease risk index, recent HSCT era, haploidentical donor type, and pre-transplant disease status independently influenced EFS and OS, whereas anti-thymocyte globulin administration significantly improved moderate-to-severe chronic GVHD, leukemia-free survival. This nationwide real-world analysis demonstrated comparable outcomes between myeloablative TBI-based and chemotherapy-based conditioning regimens in pediatric patients with ALL. These findings may inform the development of improved treatment strategies for this patient population.