The effect of threosulfan-based versus busulfan-based preparation regimens on transplant outcomes

Background: Allogeneic hematopoietic stem cell transplantation is a curative therapy for malignant and non-malignant hematologic disorders. Conditioning regimens, such as those based on busulfan, are utilized to promote engraftment. Busulfan-based regimens are commonly employed but exhibit significant toxicity, leading to interest in alternate drugs such as treosulfan, which may offer a superior safety profile while preserving efficacy. Methods: This retrospective study examined 240 adult patients diagnosed with acute myeloid leukemia or acute lymphoblastic leukemia who received allogeneic hematopoietic stem cell transplantation at nine transplantation centers in Türkiye from 2010 to 2024. Patients underwent either a busulfan-based or treosulfan-based conditioning regimen. Results: Engraftment was effective in both groups, with neutrophil engraftment happening earlier in the busulfan group (13 days vs. 15 days, p = 0.001). The incidence of veno-occlusive disease was significantly higher in the busulfan group (10.1 % vs. 0.9 %, p = 0.002). Cytomegalovirus infections were more prevalent in the busulfan group (51.2 % vs. 26.1 %, p < 0.001). Acute graft versus host disease occurred more frequently in the busulfan group (27.9 % vs. 18.9 %, p = 0.128); nonetheless, this difference did not reach statistical significance. No significant differences in relapse rates were detected through the groups. The overall survival was not reached in the busulfan group, while the treosulfan group demonstrated an overall survival of 40 months. Conclusion: Treosulfan-based conditioning regimens demonstrate similar efficacy to busulfan-based regimens while presenting a more acceptable toxicity profile. Treosulfan-based regimens also show a lower occurrence of veno-occlusive disease and cytomegalovirus infections.