By blocking the development of new blood vessels, researchers are hoping to cut off the tumor's supply of oxygen and nutrients, and therefore its continued growth and spread to other parts of the body. About 20 angiogenesis inhibitors are currently being tested in human trials. Three are in phase III testing and the results for one are expected by the end of 1999. In phase III trials, hundreds of people around the country are assigned at random to receive either the new treatment or the standard treatment. In normal tissue, new blood vessels are formed during tissue growth and repair, and the development of the fetus during pregnancy.
Blood vessels supply tissues with oxygen and nutrients necessary for survival and growth.
Endothelial cells, the cells that form the walls of blood vessels, are the source of new blood vessels and have a remarkable ability to divide and migrate. The creation of new blood vessels occurs by a series of sequential steps. Eventually, strings of new endothelial cells organize into hollow tubes, creating new networks of blood vessels that make tissue growth and repair possible. Most of the time endothelial cells lie dormant. But when needed, short bursts of blood vessel growth occur in localized parts of tissues.