Fig. 1

Tumor-induced angiogenesis. Angiogenesis, the formation of new blood vessels from preexisting blood vessels during tumor-induced angiogenesis, can be divided into three phases. Angiogenic growth factors such as basic fibroblast growth factor (bFGF) or vascular endothelial growth factor (VEGF) are secreted from tumor cells. Tumor-secreted growth factors induce cell proliferation, cell invasion, expression of integrin αvβ3 on vascular cells, and matrix degradation of surrounding extracellular matrix. The proteolytic degradation of the surrounding matrix microenvironment is a crucial step leading to new blood vessel growth and the maturation of the newly sprouted blood vessels.