EPHA3 and cancer: To investigate the effect of ephrin coexpression on Eph receptor signaling in cancer cells, we examined EphA3 (an Eph receptor for which inhibitory cis interactions with ephrin-As have been extensively studied in neurons [17,18,20]) and EphA2 (the EphA receptor most widely expressed in cancer cells [1,26-28] but for which the effects of cis interactions were not previously investigated).