Angiogenesis in colorectal cancer.

Angiogenesis is a complicated multistep process involving the breakdown of the endothelial cell basement membrane, digestion of the extracellular matrix, proliferation and migration of endothelial cells toward the angiogenic stimulus, and formation of functioning capillaries. This neovascular network not only provides nutrients for an expanding tumor mass but also a means of dissemination to sites far removed from the primary tumor site. The entire process is mediated by cytokines or growth factors released either by the tumor cells themselves or by endogenous cells within the microenvironment surrounding the tumor. The literature has conclusively shown that those lesions with high angiogenesis scores or microvessel densities are associated with a higher risk of metastases, recurrence, and early patient death. This is especially so for colorectal cancer. Antiangiogenesis therapy holds promise for the future and, in the adjuvant setting, has many theoretical advantages over conventional cytotoxic chemotherapy.