Angiogenesis is the formation of new blood vessels from the existing vascular network. It is a complex, multi-step process involving extracellular matrix remodeling, endothelial cell migration and proliferation, capillary differentiation, and anastomoses. Angiogenesis is crucial for tumor progression and metastasizing. Intratumor microvessel density is believed to reflect the degree of angiogenesis in carcinomas. Angiogenesis is also very important in many preneoplastic lesions.