Objective To evaluate the efficacy and safety of IBUCy (idarubicin, busulfan, and cyclophosphamide) and FABC (fludarabine, cytarabine, busulfan, and cyclophosphamide) conditioning regimens followed by allogeneic hematopoietic stem cell transplantation (allo-HSCT) for the treatment of medium-to-high risk acute myelocytic leukemia (AML).

Methods We retrospectively analyzed data of 49 patients with medium-to-high risk AML who received IBUCy (n=17) or FABC (n=32) conditioning regimens followed by allo-HSCT between January 2015 and December 2021 at The First Affiliated Hospital of Chongqing Medical University. Hematopoietic reconstruction time, adverse events, and survival outcomes were compared between the two groups to assess the efficacy and safety of the two regimens. Additionally, we analyzed factors that may be associated with prognosis.

Results Hematopoietic reconstruction was successful in all 49 patients. No significant differences were observed between the two groups in terms of hematopoietic reconstruction time. Similarly, no significant differences were observed in the 5-year progression-free survival (PFS) and overall survival (OS) rates between the two groups. The incidence rates of oral mucositis, nausea and vomiting, diarrhea (≥grade 3 based on CTCAE v5.0), and chronic graft-versus-host disease (GVHD) were significantly higher in the IBUCy group than that in the FABC group. However, the incidence rate of hemorrhagic cystitis in the FABC group was significantly higher than that in the IBUCy group. The time from diagnosis to allo-HSCT >6 months and being minimal residual disease (MRD)-positive before transplantation were identified as the risk factors for PFS (P=0.019 and P=0.048, respectively). Patients who were MRD-negative before transplantation had significantly longer PFS when treated with the IBUCy conditioning regimen (P=0.039).

Conclusions Both IBUCy and FABC conditioning regimens prior to allo-HSCT are safe and effective for treating medium-to-high risk AML. Allo-HSCT should be performed as soon as possible when patients achieve their first complete remission. Patients with an MRD-negative status before transplantation tend to have longer PFS. Compared with the FABC regimen, the IBUCy regimen has some advantages; however, attention should be given to the prevention and management of gastrointestinal adverse events and chronic GVHD.