AbstractDefinite cure remains exceptional in myeloma patients even after high-dose chemotherapy (HDCT) with melphalan (Mel) and autologous stem cell transplantation (ASCT). Thus, improving efficacy of HDCT in MM remains an unresolved issue. This randomized phase II trial compared standard 200 mg/m² Mel HDCT to experimental HDCT with 200 mg/m² bendamustine, given both at days −4 and −3, combined with 100 mg/m² melphalan at days −2 and −1 (BenMel) before ASCT as first-line consolidation in myeloma patients. The primary endpoint aimed to identify at least a 15% improvement in the complete remission rate (stringent CR + CR) after HDCT with BenMel compared with Mel alone. A total of 120 MM patients were 1:1 randomized. The rate of sCR/CR after ASCT was higher in BenMel than in Mel treated patients (70.0% vs. 51.7%; p = 0.039). Three patients in the BenMel group (5.0%) had reversible acute renal insufficiency compared with none in Mel patients. Minimal residual disease negativity (<10-5) by flow cytometry was observed in 26 (45.6%) BenMel patients and 22 (37.9%) in the Mel group (p = 0.375). Our data suggest that BenMel HDCT is safe and improves the sCR/CR rate compared with standard Mel alone.