Normal tissues of the body maintain their blood supply by an orderly and efficient vascular network. These networks are organized with mature, evenly distributed, vessels to allow adequate circulation of oxygen and other nutrients to all cells.
Cancerous tumour growth is restricted to about 1mm from the blood vessel due to lack of oxygen and nutrients. Therefore, for tumour growth and metastatic spread to occur the tumour must develop its own blood supply network. This process is called angiogenesis .