[Tumor angiogenesis]

Tumor angiogenesis is a very important process for growth and proliferation of most solid tumors. It insures the delivery of feeding molecules as well as the elimination of degradation products and allows tumoral cells to escape from the primary tumor site and the further establishment of metastases. Tumor neovascularisation is the result of a cascade of events primarily related to the properties of endothelial cells of capillaries. The main steps are: a) degradation of capillary basal lamina and destruction of the surrounding tissues, b) endothelial cell proliferation and c) endothelial cell migration towards the tumor site. A number of substances either synthetic or of natural origin are known to stimulate one of the above mentioned steps and/or to induce the production of factors which, in turn, stimulate one or several steps of the cascade. Such molecules can also be synthesized by tumoral cells; indeed they have often been evidenced in the fluids surrounding the tumor site. Many factors remain to be identified and their mechanism of action wait to be elucidated. However, it is already clear that several molecules are involved in the various steps of tumor angiogenesis. They display a coordinated sequential action and their synthesis is induced and controlled by the tumor itself. Amongst others, the following molecules play a role in tumor angiogenesis: degradative enzymes, E-prostaglandins, specific oligopeptides, fibronectin and heparin. Furthermore, several metal cations are also involved in tumor angiogenesis.