Angiogenesis is the development of small blood vessels. It can be formation in the normal healing process, benign tumors and so on, but, the same supply is necessary for bad tumors too. A blood supply is needed for oxygen and nutrients which allows spread to surrounding tissues and of course, mets.
A lot is being done in this part of cancer research. If all this wonderful research discovers a way to prevent it, cures will become common place for so many types of cancer. Hope that answers you question.