High-dose bendamustine and melphalan conditioning for autologous stem cell transplantation for patients with multiple myeloma.

High-dose melphalan (MEL200) followed by autologous stem cell transplantation (ASCT) remains a standard of care for multiple myeloma (MM). Bendamustine induces responses in MM resistant to other alkylators. Our prior Phase I trial adding bendamustine to MEL200 transplant conditioning resulted in no additional toxicity. We now report a single-arm, phase II study that evaluated the efficacy of bendamustine 225 mg/m ² with MEL200 conditioning for ASCT in 18 patients with newly diagnosed MM (NDMM) and 17 with relapsed or refractory MM (RRMM). The primary end point was the complete response (CR/sCR) rate at day+ 100. Sample size was determined according to Simon's two-stage design. At stage 1, sixteen patients entered the study. As there were eight patients with CR/sCR, enrollment increased to 28 patients. Sixteen out of the first 28 evaluable patients achieved CR/sCR, meeting the design criteria. Enrollment was then expanded to a total of 35 patients. 51% achieved a CR/sCR. After a median follow-up of 65 months, 21 patients progressed, including 7 deaths. The median PFS for NDMM and RRMM was 48 and 45 months, respectively. Bendamustine/MEL200 conditioning resulted in excellent overall and depth of response as well as PFS, particularly in the RRMM patients, and is worthy of further investigation (NCT00916058).