Improved post-transplant outcomes for elderly acute myeloid leukemia patients conditioned with FLU/BU4 rather than conventional MAC regimens.

It is uncertain whether FLU/BU4 regimens, classified as myeloablative conditioning (MAC), improve prognosis compared to conventional MAC regimens (conv-MAC) such as CY/TBI and BU/CY. We compared FLU/BU4 with conv-MAC among 6551 patients (FLU/BU4 905, conv-MAC 5646), including acute myeloid leukemia (AML) patients aged 16-59 who received a first allogeneic transplantation from the Japanese nationwide registry. The primary endpoint was overall survival (OS), while secondary endpoints were treatment-related mortality (TRM) and relapse at 3 years. Results indicated comparable OS for conv-MAC regimens among the entire cohort (3-year OS: FLU/BU4 50.4% vs. conv-MAC 55.4%, p < 0.001). Subgroup analysis focusing on elderly patients (aged 50-59) indicated that FLU/BU4 showed a statistically significant improvement in OS (47.0% vs. 42.8%, p = 0.036). Notably, for patients in this cohort transplanted at complete remission (CR), FLU/BU4 demonstrated a substantial advantage over conv-MAC with superior OS (HR 0.75, p = 0.046), lower TRM (HR 0.66, p = 0.035), and comparable relapse (HR 0.84, p = 0.390). These benefits were not observed in elderly patients transplanted at non-CR or in other age groups. In summary, our findings suggest that FLU/BU4 regimen, rather than conv-MAC, may be preferable in MAC-tolerant AML patients, aged 50-59 at CR status. This treatment improves survival by reducing TRM without increasing relapse risk.