Ephrin-A1, also known as EFNA1, is encoded by the EFNA1 gene in humans, which encodes members of the Eph family. The ephrins and Eph related receptors form the largest receptor tyrosine kinase subfamily and are involved in regulating the development of the nervous and hematopoietic systems. According to their structure and sequence relationship, ephrins can be divided into ephrin-A (EFNA) class and ephrin-B (EFNB) class. The Ephrin-A ligand binds to the EphA receptor and is anchored to the plasma membrane through glycosylphosphatidylinositol (GPI) connections. The ephrin-B ligand binds to the EphB receptor and is anchored to the plasma membrane through a transmembrane domain. Ephrin-A1 and one of its receptors, EphA2, are expressed in xenograft endothelial cells and tumor cells, and can play a role in human cancer to some extent by influencing tumor neovascularization.