Abstract

Angiogenesis is controlled by the balance between molecules that have positive and negative regulatory activities and this concept has led to the notion of the angiogenic switch, which depends on an increased production of one or more positive regulators of angiogenesis [1]. Most human tumors arise and remain in situ without angiogenesis for a long time before switching to an angiogenic phenotype, through a pre-neoplastic stage as occurs in breast and cervical carcinomas, which becomes neovascularized before the malignant tumor appears. Activation of the angiogenic switch has been attributed to the synthesis or release of angiogenic factors, and accordingly to the balance hypothesis, the level of angiogenesis inducers and inhibitors regulates angiogenesis in physiological conditions. This balance is altered in pathological conditions, including tumors, as a consequence of an increase bioavailability or activity of the inducer proteins, or reducing the concentrations of endogenous angiogenesis inhibitors. Restore of this balance may induce a normalization of structure of blood vessels.

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