Tumor angiogenesis: biology and therapeutic prospects

Angiogenesis is now recognized as a critical process in tumor progression and is required for solid tumors to grow beyond a few millimeters in size. The transition from a non angiogenic to an angiogenic phenotype and subsequent tumor vascularization is not well understood but is likely to involve angiogenic stimulators and inhibitors. Regulation of vascular growth also involves complex interactions of extracellular matrix molecules, proteolytic enzymes and cell adhesion molecules. Each step in the angiogenic process represents a potential target for therapeutic anticancer strategies. Antiangiogenic compounds have proven very successful as cancer treatments in murine animal models and demonstrated utility in treating humans cancers in clinical trials. These agents exhibit reduced toxicity and a decreased likelihood for the development of drug resistance compared to conventional chemotherapies. This review summarizes current knowledge of tumor angiogenesis and the factors involved, and, in addition, presents an overview of current and future antiangiogenic therapies.