BACKGROUND: Vascular endothelial growth factor is a key promoter of angiogenesis and disease progression in epithelial ovarian cancer. Bevacizumab, a humanized anti-vascular endothelial growth factor monoclonal antibody, has shown single-agent activity in women with recurrent tumors. Thus, we aimed to evaluate the addition of bevacizumab to standard front-line therapy. METHODS: In our double-blind, placebo-controlled, phase 3 trial, we randomly assigned eligible patients with newly diagnosed stage III (incompletely resectable) or stage IV epithelial ovarian cancer who had undergone debulking surgery to receive one of three treatments. All three included chemotherapy consisting of intravenous paclitaxel at a dose of 175 mg per square meter of body-surface area, plus carboplatin at an area under the curve of 6, for cycles 1 through 6, plus a study treatment for cycles 2 through 22, each cycle of 3 weeks' duration. The control treatment was chemotherapy with placebo added in cycles 2 through 22; bevacizumab-initiation treatment was chemotherapy with bevacizumab (15 mg per kilogram of body weight) added in cycles 2 through 6 and placebo added in cycles 7 through 22. Bevacizumab-throughout treatment was chemotherapy with bevacizumab added in cycles 2 through 22. The primary end point was progression-free survival. RESULTS: Overall, 1873 women were enrolled. The median progression-free survival was 10.3 months in the control group, 11.2 in the bevacizumab-initiation group, and 14.1 in the bevacizumab-throughout group. Relative to control treatment, the hazard ratio for progression or death was 0.908 (95% confidence interval [CI], 0.795 to 1.040; P = 0.16) with bevacizumab initiation and 0.717 (95% CI, 0.625 to 0.824; P<0.001) with bevacizumab throughout. At the time of analysis, 76.3% of patients were alive, with no significant differences in overall survival among the three groups. The rate of hypertension requiring medical therapy was higher in the bevacizumab-initiation group (16.5%) and the bevacizumab-throughout group (22.9%) than in the control group (7.2%). Gastrointestinal-wall disruption requiring medical intervention occurred in 1.2%, 2.8%, and 2.6% of patients in the control group, the bevacizumab-initiation group, and the bevacizumab-throughout group, respectively. CONCLUSIONS: The use of bevacizumab during and up to 10 months after carboplatin and paclitaxel chemotherapy prolongs the median progression-free survival by about 4 months in patients with advanced epithelial ovarian cancer. (Funded by the National Cancer Institute and Genentech; ClinicalTrials.gov number, NCT00262847.) Copyright © 2011 Massachusetts Medical Society. All rights reserved.