Treosulfan Conditioning for Allogeneic Transplantation in Multiple Myeloma Improved Overall Survival in Upfront Hematopoietic Stem Cell Transplantation — a Large Retrospective Study By the Chronic Malignancies Working Party of the EBMT

Background Allogeneic hematopoietic stem cell transplantation (AlloSCT) for treatment of multiple myeloma (MM) is controversial mainly due to high non-relapse mortality (NRM) with myeloablative conditioning. However, AlloSCT is probably the only treatment that result in cure of a small fraction of patients. Treosulfan is a prodrug of a bifunctional alkylating agent which has both myelotoxic and immunosuppressive properties. Conditioning regimes with treosulfan have been tried in various hematologic neoplasia such as AML and MDS indicating low NRM and increased progression free survival (PFS). Previous studies on use of treosulfan condition in AlloSCT for MM indicated feasibility, stable engraftment and low NRM. In the present study we have analysed the results of low and high dose treosulfan respectively on OS, RFS, relapse incidence and NRM as well as results of Treosulfan conditioning compared to non-Treosulfan reduced intensity conditioning (RIC) and non-Treosulfan myeloablative conditioning (MAC). Patients and Methods We conducted a retrospective analysis of 4544 patients with MM undergoing AlloSCT 2008-2016 reported to the EBMT data registry. Out of 537 patients receiving Treosulfan based conditioning the impact of dose could be analysed in 441. Three hundred and twenty-seven patients received a total dose of >36g/m2 and 114 36g/m2, showed a tendency for improved OS and RFS compared to the lower dose treosulfan as well as RIC and MAC (table 2) respectively. In multivariate analysis of upfront transplanted patients, with a model adjusted for ISS score at diagnosis, age, Karnofsky score, response at AlloSCT, interval between diagnosis and transplant, donor type and donor - patient sex match,