Cancer cells die off quickly if they do not have a blood supply. Cancers can grow only about 2 millimeters and then will stop growing unless they have more blood vessels. There are certain proteins that function to promote the development of new blood vessels. These proteins are specific growth factors that have important roles during development. An embryo, for example, needs new blood vessels that can grow all the way to the arms and legs, in order to develop fingers and toes distally. In the case of an injury, one needs blood vessels to grow and heal it. This explains why an injured area appears red. One such protein, which stimulates blood vessel growth, is known as vascular endothelial growth factor or vascuolotropin. This is secreted by the cancer cells and then binds to their specific receptor on the blood vessels and tells them to make more cells. This will initiate the process of angiogenesis - "angio" means vessels and "genesis" which means growth. On a microscopic view, some tumors have more blood vessels than others do. The more blood vessels a tumor has, the more blood supply it has, which in turn facilitates its growth. Thus, the more chances the cancer has of spreading, because there are more "roads" to spread out on. Some researchers think that perhaps we can measure vascular endothelial growth factor in the blood or in the breast duct fluid to see if there are new blood vessels growing.
A researcher from Boston made the astonishing discovery that cancers actually secrete not only growth promoting proteins, but also growth inhibiting ones (angiogenic inhibitors). These are substances that keep metastasis under control by inhibiting the growth of new blood vessels. Thus, when the primary cancer is removed, the metastasis grows more because the angiogenic inhibitors are also removed. It seems quite odd that a cancer would produce something from itself to stop it from growing. One would always think it is in the nature of cancer to want to spread and metastasize. Cancer will grow in its own area, but will keep any cells from growing in other organs. The idea is fanciful, but cancers do not seem to like having rivals. This is definitely not to suggest that if you have a cancer, you should ignore it because in won't spread unless you undergo surgery. For one thing, it probably isn't true for all cancers. For another, the process of metastasis after cancer surgery is far from absolute. It doesn't stop the cancer from spreading; it only controls the metastasis already out there.
Anti-angiogenic drugs are now being tested in humans for breast cancer therapy. One of these is thalidomide. This drug blocks the growth of new blood vessels. This is why when pregnant women in the 60s took it to treat insomnia; their children were often born without arms and legs. But if you are not pregnant and you're an adult who does not need more blood vessels, then you may want to ask your oncologist about treatment options involving thalidomide. Several anti-angiogenesis drugs being tested nowadays may not even have the adverse effects caused by thalidomide. Some new drugs that were developed for the treatment of arthritis, such as cyclooxygenase 2 inhibitors are also anti-angiogenic. These drugs are being tested now for breast cancer prevention.
