Individualized busulfan dosing improves outcomes compared to fixed‐dose administration in pre‐transplant minimal residual disease‐positive acute myeloid leukemia patients with intermediate‐risk undergoing allogeneic stem cell transplantation in CR

Pre‐transplant minimal residual disease (MRD) impacts negatively on post‐transplant relapse risk in acute myeloid leukemia (AML). Therapeutic drug monitoring by calculating area under the curve (AUC) was developed to optimize busulfan (Bu) exposure. Here, we compared post‐transplant outcomes after individualized versus fixed busulfan dosage in intermediate‐risk AML who achieved CR prior to allograft focusing on pre‐transplant flow‐MRD. Eighty‐seven patients (median, 56 years) with intermediate‐risk AML and pre‐transplant flow‐MRD ("different from normal") were included. Thirty‐two patients received individualized busulfan; 54 fixed dosages. Individualized dosage was adjusted in 25/32 patients: increased, n = 18/25 (72%); decreased: n = 7/25 (28%). After median follow‐up of 27 months, we observed lower 3‐year relapses (6%, 2%–19% vs. 35%, 23%–49% p = 0.02), improved 3‐year leukemia‐free survival (LFS) (78%, 54%–91% vs. 55%, 40%–70% p = 0.009) and − overall survival (OS) (82%, 60%–93% vs. 69%, 54%–81% p = 0.05) after individualized compared to fixed Bu. Non‐relapsed mortality (NRM) and acute graft versus host disease (GvHD) were not different. In multivariate analysis, fixed Bu showed unfavorable impact on OS (hazard ratio [HR] 4.6, p = 0.044), LFS (HR 3.6, p = 0.018) and relapses (HR 3.6, p = 0.033). Fixed Bu also had unfavorable impact on LFS (3.6, 1.1–12.6, p = 0.041) in pre‐transplant MRD‐positive patients. Individualized, AUC‐based, busulfan is associated with lower relapses in intermediate‐risk AML patients allografted in CR and may overcome pre‐transplant MRD‐positivity. [ABSTRACT FROM AUTHOR]