Tumor growth and metastasis are facilitated by the formation of new blood vessels, a process known as angiogenesis. The blood vessels formed around the tumor supply it with oxygen and nutrients, which together support its progression. Moreover, the newly formed blood vessels serve as channels through which tumor cells metastasize to distant organs. Tumor blood vessels, and especially the endothelial cells lining tumor blood vessels (tumor endothelial cells, TECs), have therefore gained interest as targets in cancer therapy. Although newly formed tumor blood vessels originate from pre-existing, normal vessels, they have a distinctively abnormal phenotype, including important morphological alterations. The balance between the angiogenic stimulators and inhibitors regulates angiogenesis in the tumor microenvironment. Furthermore, TECs constitute a heterogeneous population, exhibiting characteristics induced largely by tumor microenvironmental factors. In this chapter we review recent studies on TEC abnormalities regarding to cancer progression and consider the therapeutic implications thereof.
Keywords: Angiogenesis, Angiogenic factor, Anti-angiogenic therapy, Basement membrane, Blood vessel, Cancer, Drug resistance, Endothelial cell, Heterogeneity, Hypoxia, Invasion, Metastasis, Migration, Pericyte, Side effect, Tumor, Tumor angiogenesis, VEGF.