Other cytokines and growth factors also play an important role in promoting angiogenesis. Some of these act directly on endothelial cells, whereas others stimulate adjacent in-
flammatory cells. Some can cause migration but not division of endothelial cells such as angiotropin, macrophage-derived factor, and II, or stimulate proliferation such as EGF, acidic and basic fibroblast growth factors (aFGF, bFGF), transforming growth factor II (II), and VEGF (67). Tumors secrete these factors, which stimulate endothelial migration, proliferation, proteolytic activity, and capillary morphogenesis (68).