Cancer cells promote angiogenesis early in tumorigenesis because cancer cells require oxygen and nutrients for their survival they need to be supported by blood vessels. The angiogenic switch is driven by several proangiogenic factors, vascular endothelial growth factor (VEGF), interleukin-8 (IL-8), basic fibroblast growth factor (bFGF) and others. These proangiogenic factors are released from not only cancer cells but also various stromal cells by various stimulations, mutations or inflammation. From our experimental results using human lung cancer cell lines, survival factors in each cancer cell line are different. This makes cancer therapy difficult. Various angiogenesis inhibitors have been developed to block tumor angiogenesis. However we need to think how and when to use angiogenesis inhibitors together with conventional chemotherapeutic agents.