PURPOSE: This phase III study compared docetaxel with mitomycin plus vinblastine (MV) in patients with metastatic breast cancer (MBC) progressing despite previous anthracycline-containing chemotherapy. PATIENTS AND METHODS: Patients (n = 392) were randomized to receive either docetaxel 100 mg/m² intravenously (IV) every 3 weeks (n = 203) or mitomycin 12 mg/m² IV every 6 weeks plus vinblastine 6 mg/m² IV every 3 weeks (n = 189), for a maximum of 10 3-week cycles. RESULTS: In an intention-to-treat analysis, docetaxel produced significantly higher response rates than MV overall (30.0% v 11.6%; P < .0001), as well as in patients with visceral involvement (30% v 11%), liver metastases (33% v 7%), or resistance to previous anthracycline agents (30% v 7%). Median time to progression (TTP) and overall survival were significantly longer with docetaxel than MV (19 v 11 weeks, P = .001, and 11.4 v 8.7 months, P = .0097, respectively). Neutropenia grade 3/4 was more frequent with docetaxel (93.1% v 62.5%; P < .05); thrombocytopenia grade 3/4 was more frequent with MV (12.0% v 4.1%; P < .05). Severe acute or chronic nonhematologic adverse events were infrequent in both groups. Withdrawal rates because of adverse events (MV, 10.1%; docetaxel, 13.8%) or toxic death (MV, 1.6%; docetaxel, 2.0%) were similar in both groups. Quality-of-life analysis was limited by a number of factors, but results were similar in both groups. CONCLUSION: Docetaxel is significantly superior to MV in terms of response, TTP, and survival. The safety profiles of both therapies are manageable and tolerable. Docetaxel represents a clear treatment option for patients with MBC progressing despite previous anthracycline-containing chemotherapy.