Angiogenesis is a vital step of tumour progression, and there has been no shortage of strategies devised to target the developing tumour vasculature. Although these approaches have not completely inhibited tumour growth in clinical trials, our understanding of the angiogenic process has improved. For this reason, this month's issue is a special 'Focus on Angiogenesis' that covers the latest advances in this field.
Recent clinical and basic research studies have taught us a great deal about the limitations of using anti-angiogenic strategies to treat cancer. For example, on page 401 Gabriel Bergers and Laura Benjamin explain how different tumour types initiate blood-vessel formation — termed the 'angiogenic switch' — at different stages of progression. On page 411, Mary Hendrix and colleagues show that cancer cells can actually mimic the activities of endothelial cells and form their own fluid-conducting meshworks. This is one reason that many tumours are resistant to reagents designed to target vascular endothelium. And, as Raghu Kalluri explains on page 422, we are just beginning to understand the elements of the tumour environment, such as basement membranes, that provide a wide array of pro- and anti-angiogenic signals. These signals provide an entirely new source of therapeutic targets.
