Despite advances in detection and therapy, recurrent or metastatic disease will develop in approximately 30% of women with breast cancer. 1 The clinical course of metastatic breast cancer (MBC) is heterogeneous, owing to large differences in the growth rate and responsiveness to systemic therapy. 2 Many patients with MBC respond to their first treatment with endocrine or chemotherapy agents, but the disease nearly always progresses and the probability of a response decreases with each course of treatment. 2 Average survival in patients with MBC is 2 years to 4 years after diagnosis. 3-6

Antiangiogenesis is a new strategy for treating breast cancer. The invasion and metastasis of breast cancer and other solid tumors depend on angiogenesis, a process that is stimulated by the release of proangiogenic peptides, including vascular endothelial growth factor (VEGF). 7, 8 Bevacizumab is a humanized monoclonal antibody that binds to and neutralizes the VEGF-A ligand, thereby inhibiting the development of new tumor vasculature and the maintenance of existing vasculature. 9 Bevacizumab also induces vascular normalization, as evidenced by greater tumor uptake of chemotherapy agents after anti-VEGF therapy in preclinical colon xenograft models. 10 Antiangiogenesis therapy has been studied in phase 1, 2, and 3 clinical trials in more than 5000 patients with advanced carcinomas, 11 and the efficacy of bevacizumab-containing regimens has been shown in first-line trials in MBC, 12 colorectal cancer, 13 and non–small-cell lung cancer (NSCLC), 14 as well as in later lines of therapy for colorectal cancer, 15 ovarian cancer, 16 and NSCLC. 17