Tandem Conditioning-Based Myeloablative Hematopoietic Stem Cell Transplantation for Pediatric Patients with Refractory Myeloid Leukemias.

Survival outcomes of pediatric patients with refractory myeloid leukemias who undergo allogeneic hematopoietic stem cell transplantation (HSCT) remain poor. We investigated the safety and efficacy of a tandem conditioning-based myeloablative HSCT for these high-risk patients. We retrospectively analyzed 10 patients with refractory myeloid leukemias (acute myeloid leukemia, n = 9; juvenile myelomonocytic leukemia blast phase, n = 1), who underwent HSCT following tandem conditioning between 2021 and 2024. All patients were in nonremission at the time of transplantation. Tandem conditioning consisted of FLAG (fludarabine, cytarabine, and granulocyte-colony stimulating factor), followed by myeloablative busulfan and melphalan. Neutrophil and platelet engraftment were observed in 10 patients at a median of 18 days and in 8 patients at a median of 92 days post-transplantation, respectively. All but 1 patient achieved complete remission at the initial post-transplant evaluation performed at a mean of 52 days after HSCT (range, 33 to 91 days). With a median follow-up of 23.2 months for surviving patients, the estimated 2-year leukemia-free survival rate was 70.0 ± 14.5% (n = 7 of 10). The 100- day cumulative incidence of grade II-IV acute graft-versus-host disease (GVHD) and the 1-year cumulative incidence of chronic GVHD were 50.0 ± 17.3% and 40.0 ± 17.2%, respectively. Significant early post-HSCT complications included cytomegalovirus DNAemia (n = 7), veno-occlusive disease (n = 4), and hemorrhagic cystitis (n = 4). Although post-HSCT complications were significant, tandem conditioning-based myeloablative HSCT demonstrated promising remission and survival rates in pediatric patients with refractory myeloid leukemias.