To grow beyond a certain size, tumors need a system to bring in nutrients andtake out wastes. The cancer cells that make up a tumor attract blood vesselsto grow into the tumor mass. The blood vessels then nourish the tumor just likeany organ in the body.
Robert Weinberg, Ph.D
Whitehead Institute for Biomedic Research
Cancer cells have to learn how to become angiogenic, that is to say attract bloodvessels to grow into the tumor mass, thereby providing the tumor with nutrientsand glucose and oxygen and evacuating metabolic wastes and carbon dioxide.
In 2000, Douglas Hanahan (shown below) and Robert Weinberg published a paper in Cell, "The Hallmarks of Cancer," which identified some organizingprinciples of cancer cell development.
As a cell, you need oxygen to breathe, the same way your organism does. Thatdividing nest of cells will in some sense suffocate from lack of nutrients andoxygen and from their own waste unless they have a blood supply. It is now clearthat induction and new blood vessel growth -- the process of angiogenesis --is critical for almost all cancers, some less then others. Perhaps the leukemiasand the blood-borne ones are less angiogenesis dependent, but it may be thatall cancers, in some sense, activate the vascular system to help support it.