Impact of conditioning regimen on outcomes of young AML patients ( < 40 years) undergoing HCT in complete remission, with transplant conditioning intensity score of 3.5-4.0. A study from the acute leukemia working party of the European Society for Blood and Marrow Transplantation

The optimal myeloablative conditioning regimen for adolescents and young adults with acute myeloid leukaemia (AML) is currently unknown. In this retrospective analysis conducted on AML patients aged 18-40 years, in complete remission (CR), who received an allogeneic hematopoietic cell transplantation (HCT) we compared outcomes of different conditioning regimens. A total of 4323 patients, with median age of 30.9 years, transplanted from 2010 to 2022, received one of four regimens: high-dose total body irradiation (TBI)-based (n = 1031), thiotepa-busulfan (Bu)-fludarabine (Flu) (TBF) n = 219, Bu-Flu (n = 1100), and Bu-cyclophosphamide (Cy) (n = 1973). Prolonged OS and PFS for Bu-Flu (hazard ratio [HR] 0.73, 95% CI 0.57–0.92, p = 0.008; HR 0.78, 95% CI 0.64–0.94, p = 0.01), and TBF (HR 0.59, 95% CI 0.38-0.92, p = 0.02; HR 0.67, 95% CI 0.47–0.94, p = 0.02), respectively, as well as less RI for both Bu-Flu (HR 0.77, 95% CI 0.63–0.95, p = 0.01), and TBF (HR 0.68, 95% CI 0.47–0.99, p = 0.046). In conclusion, young adult AML patients seem to benefit from high dose TBI-free regimens, in terms of survival and toxicity, with four major myeloablative regimens. TBF and Bu-Flu were associated with better clinical outcomes, partly reflecting the general improvement in supportive therapies and patient selection introduced in recent years. Prospective clinical trials are warranted.