Targeting the tumor vasculature: a strategy to improve radiation therapy

A continuously expanding vasculature is an essential requirement of a growing neoplastic mass. The blood-vessel network provides not only nutritional support and waste product management, but also offers opportunities for the secondary spread of tumor cells. Given its crucial role in tumor development, growth and spread, considerable efforts have been spent on developing therapeutic strategies that compromise the growth and/or function of the tumor neovasculature. Two primary approaches are being pursued. Angiogenic inhibitors seek to interrupt the process of angiogenesis to prevent new tumor blood-vessel formation. Vascular disrupting agents aim to cause direct damage to the existing tumor endothelium. Lead agents in both categories have now advanced into clinical trials. Still, their greatest utility may ultimately lie in combinations with conventional anticancer therapies. Indeed, the application of such strategies as adjuvants to conventional radiation treatments offers unique opportunities to develop more effective cancer therapies.