Roles of main pro- and anti-angiogenic factors in tumor angiogenesis.

Tumor growth without size restriction depends on vascular supply. The ability of tumor to induce new blood-vessel formation has been a major focus of cancer research over the past decade. It is now known that members of the vascular endothelial growth factor and angiopoietin families, mainly secreted by tumor cells, induce tumor angiogenesis, whereas other endogenous angiogenic inhibitors, including thrombospondin-1 and angiostatin, keep tumor in dormancy. Experimental and clinical evidence has suggested that the process of tumor metastasis depends on angiogenesis or lymphangiogenesis. This article summarizes the recent research progress for some basic pro- or anti-angiogenic factors in tumor angiogenesis.