Clinical Efficacy and Safety of a Modified Conditioning Regimen Reducing the Dosage of Busulfan and Adding Thiotepa in Allogeneic Hematopoietic Stem Cell Transplantation for Pediatric Acute Myeloid Leukemia.

Objective: This study aimed to investigate the efficacy and safety of allogeneic hematopoietic stem cell transplantation (allo-HSCT) with a conditioning regimen that reduces the dosage of busulfan and incorporates thiotepa in children with acute myeloid leukemia (AML).

Methods: A retrospective analysis was conducted on 55 pediatric patients with AML who underwent allo-HSCT at Hunan Children's Hospital from December 2019 to December 2023. Group A (n = 33) included patients with thiotepa in the conditioning regimen, while Group B (n = 22) included patients without thiotepa. Conditioning regemen of Group A was modified to reduce 1 day dosage of busulfan and add an additional dose of thiotepa at 10 mg/kg.

Results: With a median follow-up of 31 months, the OS for all patients was 94.5%. Group A had a higher survival rate compared to Group B, though the difference was not statistically significant (96.9% vs 90.9%, P = .388). For patients who were measurable residual disease positive before transplantation, the OS in Group A was significantly higher than in Group B (100% vs 75%, P = .039). The total relapse rate was 5.45%, with no significant difference between the groups (Group A 6% vs Group B 4.55%, P = .648). The non-relapse mortality was 1.8%, with only 1 death due to severe sinusoidal obstruction syndrome (SOS) in Group B. The incidence rates of acute graft-versus-host disease (aGVHD), severe aGVHD, SOS, and transplant-associated thrombotic microangiopathy (TA-TMA) were lower in Group A, particularly for aGVHD and severe aGVHD (30.3% vs 45.4%, P = .252; 12.1% vs 27.3%, P = .175), although these differences were not statistically significant.

Conclusion: The modified conditioning regimen demonstrated promising clinical efficacy and safety. This modified regimen has the potential to enhance the prognosis of pediatric AML patients, especially those with MRD-positive pre-transplantation.