Purpose: Effective treatment options for patients with metastatic breast cancer resistant to anthracyclines and taxanes are limited. Ixabepilone has single-agent activity in these patients and has demonstrated synergy with capecitabine in this setting. This study was designed to compare ixabepilone plus capecitabine versus capecitabine alone in anthracycline-pretreated or -resistant and taxane-resistant locally advanced or metastatic breast cancer. Patients and Methods: Seven hundred fifty-two patients were randomly assigned to ixabepilone 40 mg/m2 intravenously on day 1 of a 21-day cycle plus capecitabine 2,000 mg/m2 orally on days 1 through 14 of a 21-day cycle, or capecitabine alone 2,500 mg/m2 on the same schedule, in this international phase III study. The primary end point was progression-free survival evaluated by blinded independent review. Results: Ixabepilone plus capecitabine prolonged progression-free survival relative to capecitabine (median, 5.8 v 4.2 months), with a 25% reduction in the estimated risk of disease progression (hazard ratio, 0.75; 95% CI, 0.64 to 0.88; P = .0003). Objective response rate was also increased (35% v 14%; P < .0001). Grade 3/4 treatment-related sensory neuropathy (21% v 0%), fatigue (9% v 3%), and neutropenia (68% v 11%) were more frequent with combination therapy, as was the rate of death as a result of toxicity (3% v 1%, with patients with liver dysfunction [≥ grade 2 liver function tests] at greater risk). Capecitabine-related toxicities were similar for both treatment groups. Conclusion: Ixabepilone plus capecitabine demonstrates superior efficacy to capecitabine alone in patients with metastatic breast cancer pretreated or resistant to anthracyclines and resistant to taxanes. © 2007 by American Society of Clinical Oncology.