Primary tumors and metastases require blood vessel formation to support their continued growth and eventual metastasis. They use existing vasculature during initial growth but eventually must orchestrate the development and maintenance of new vessels--a process termed angiogenesis--to grow beyond a small size and spread. Angiogenesis is regulated by a number of soluble factors, the relative proportions of which can exacerbate or inhibit the process. Vascular endothelial growth factor (VEGF) is a potent stimulator of angiogenesis, produced by the majority of human solid tumors. Inhibitors of VEGF might have an impact on the growth and metastasis of these cancers. The relevance of this strategy to the treatment of colorectal cancer was first successfully demonstrated in human clinical trials using a monoclonal antibody against VEGF. A potent antiangiogenic soluble recombinant decoy, VEGF Trap is a protein constructed from VEGF receptor-binding domains linked to an immunoglobulin G(1) constant region. It possesses an affinity for VEGF that is significantly higher than that of the monoclonal antibody. VEGF Trap has demonstrated marked efficacy in halting angiogenesis and shrinking tumors in preclinical animal models and is currently being studied in phase I clinical trials in humans with advanced solid malignancies.