Purpose: Treosulfan was introduced recently as a conditioning agent for allogeneic blood stem-cell transplantation. The favorable nonhematologic toxicity profile at 3 x 10 g/m(2) was the basis for dose escalation in this prospective, multicenter trial.
Patients and methods: Fifty-six patients with various hematologic malignancies who were not eligible for standard conditioning were treated with one of three doses: 10 g/m(2), 12 g/m(2), or 14 g/m(2) of intravenous treosulfan, which was administered on days -6 to -4 combined with fludarabine 30 mg/m(2) on days -6 to -2. Patients in complete remission (CR; 42%) or non-CR (58%) received grafts from matched related (47%) or matched unrelated (51%) donors; one patient had a mismatched related donor (2%).
Results: No engraftment failure occurred. Overall, extramedullary toxicity and the nonrelapse mortality rate at 2 years (20%) were low and did not increase with dose. Cumulative incidence of relapse/progression reached 31%. The overall survival and progression-free survival rates were 64% and 49%, respectively, in the total study population. An inverse dose dependency of relapse incidence was indicated in the subgroup receiving transplantations from matched related donors (P = .0568).
Conclusion: Treosulfan-based conditioning was feasible at all three doses. The 3 x 14 g/m(2) dose was selected for additional studies, because it combines desired characteristics of low toxicity and a low relapse rate.