Malignant tumors cannot grow beyond a certain size without establishing blood supply to feed them with necessary nutrients and oxygen. The process of recruiting new blood vessels to the tumor is termed angiogenesis. Growth factors, mainly secreted by the tumor itself, induce angiogenesis; the most notable of these is vascular endothelial growth factor (VEGF), which helps endothelial precursor cells mature into neo-capillary forming, endothelial cells. These secrete other growth factors, like platelet derivative growth factor (PDGF), which attracts pericytes and vascular smooth muscle cells that, together, create the outer layers of capillaries.   Continue reading →