sentences:  Though the role of ephrins in developmental angiogenesis is elucidated, tumor angiogenesis remains nebulous.Based on observations in Ephrin-A2 deficient mice, Ephrin-A2 may function in forward signalling in tumor angiogenesis; however, this ephrin does not contribute to vascular deformities during development.Moreover, Ephrin-B2 and EphB4 may also contribute to tumor angiogenesis in addition to their positions in development, though the exact mechanism remains unclear.