The Eph receptor tyrosine kinases and ephrin ligands have been studied 
extensively for their roles in developmental processes. In recent years, Eph 
receptors and ephrins have been found to be integral players in cancer formation 
and progression. Among these are EphA2 and ephrinA1, which are involved in the 
development and maintenance of many different types of solid tumors. The 
function of EphA2 and ephrinA1 in tumorigenesis and tumor progression is complex 
and seems to be dependent on cell type and microenvironment. These variables 
affect the expression of the EphA2 and ephrinA1 proteins, the pathways through 
which they induce signaling, and the functional consequences of that signaling 
on the behavior of tumor cells and tumor-associated cells. This review will 
specifically focus on the roles that EphA2 and ephrinA1 play in the different 
cell types that contribute to the malignancy of solid tumors, with emphasis on 
the opportunities for therapeutic targeting.