Angiogenesis is a general term used to describe a complex process involving many systems. It can be described as the process by which new blood vessels are formed. Cancerous tumors grow at an accelerated rate resulting in the need for greater-than-normal amounts of nutrients. Exactly how this process occurs in still the subject of intense research, but much is known.
1. As the tumor grows, it "calls for" new blood vessels (which supply vital oxygen and nutrients) by sending out a series of growth factor proteins.
2. These proteins come into contact with existing blood vessels, creating pores in the outer layers.
3. The matter between the inner and outer layers of the blood vessels forms a high-pressure pocket in the surrounding tissue which is ideal for the formation of new blood vessels.
4. The inner-most layer of cells (endothelium) grows towards the tumor, eventually forming a loop, which allows for blood to flow to the tumor. A good description of this process can be found here.
A distinct problem with the newly formed blood vessels is that they are irregular in shape. This condition is called "hyper permeable" (a.k.a. "leaky"). A growing body of research is clearly pointing to MetAP2 as a key regulator of this process.
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