Two i.v. regimens, bendamustine, methotrexate and 5-fluorouracil (BMF) and cyclophosphamide, methotrexate and 5-fluorouracil (CMF) were compared as first-line therapy in a randomized, open, multicenter phase III trial including 364 patients with metastatic breast cancer (MBC). Bendamustine is an anti-neoplastic agent with alkylating, but also additional, so far unclear, mechanisms of action. We wanted to show the superiority of BMF over CMF in terms of time to progression (TTP) (primary endpoint), overall response, response duration, toxicity and quality of life (QoL). TTP was significantly longer in the BMF group (8.2 versus 6.7 months for CMF) (p=0.0071). The effect of BMF on TTP was more pronounced in the stratum 'prior adjuvant therapy, no visceral metastases' (p=0.034). Overall response rates and QoL did not significantly differ between the regimens. BMF caused more mucositis and leukopenias. Thus, bendamustine, when replacing cyclophosphamide in the CMF combination, can be expected to produce longer progression-free survival in first-line treatment of MBC.