Angiogenesis is a complex process by which new blood vessels are formed from pre-existing ones by sprouting, remodeling and expansion of primary vascular networks . In normal conditions, following this morphogenesis, the vasculature becomes largely quiescent. However, within tumors, an “angiogenic switch” is always activated, causing continuous generation of new vessels . The “angiogenic switch” is governed by pro-angiogenic and anti-angiogenic signals elicited by tumor cells or tumor microenvironment [8, 9]. When pro-angiogenic signals are activated or anti-angiogenic signals are inhibited, the “angiogenic switch” is turned on. Understanding the regulation of tumor angiogenesis is critical to developing therapeutic strategies against cancer.