EFNA3 and cancer: Here we show that Eph receptors and ephrins coexpressed in cancer cells can engage in cis interactions that inhibit Eph receptor activation by ephrins in trans. Interestingly, we detected inhibition of EphA3 activation through cis interaction with not only ephrin-A3 but also ephrin-B2, which is not an activating ligand for EphA3 [25], suggesting that cis interactions do not exhibit the same receptor-ligand selectivity as trans interactions.