Tumor blood vessels as targets for cancer therapy

Tumor growth and metastasis are dependent on angiogenesis, which is the formation of new blood vessels. The newly formed blood vessels around the tumor supply oxygen and nutrients to the tumor, supporting its progression. Moreover, these blood vessels also 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)], are important targets in cancer therapy. Since newly formed tumor blood vessels originate from pre-existing normal vessels, tumor blood vessels and TECs traditionally have been considered the same as normal vasculature. Tumor blood vessels, however, have a distinctively abnormal phenotype, including morphological alterations. Recently, it has been revealed that TECs constitute a heterogeneous population, exhibiting characteristics induced largely by tumor microenvironmental factors. Furthermore, TECs induce cancer progression through metastasis passively but also actively. This chapter will review the mechanisms underlying tumor angiogenesis and discuss the biology of TECs, offering new perspectives on treatment strategies that can target tumor blood vessels from a personalized medicine perspective.