Treosulfan-based conditioning regimens for allogeneic HSCT in children with acute lymphoblastic leukaemia

Standard myeloablative conditioning regimens for children with acute lymphoblastic leukaemia are based on total body irradiation (TBI). However, TBI causes profound short-term and long-term side effects, provoking the necessity for alternative regimens. Treosulfan combines a potent immunosuppressive and antileukaemic effect with myeloablative activity and low toxicity profile. We retrospectively studied toxicity and outcome of 71 paediatric patients with acute lymphoblastic leukaemia (ALL) undergoing haematopoietic stem cell transplantation (HSCT) following treosulfan-based conditioning aiming to identify risk factors for treatment failure and dose-depending outcome differences. Early regimen-related toxicity was low. No case of veno-occlusive disease was reported. There was no association of toxicity with age or number of HSCT. Event-free survival (EFS) of infants was significantly better compared to older children. Overall survival (OS) at 3 years was 51 % and not significantly influenced by number of HSCT (first HSCT 54 %, ≥second HSCT 44 %, p = 0.71). In multivariate analysis, OS and EFS were significantly worse for patients transplanted without complete remission (p = 0.04 and 0.004). Treatment-related mortality was low at 14 %. We conclude that treosulfan-based conditioning is a safe and efficacious approach for paediatric ALL.