To examine whether in cancer cells ephrin-A3 coexpression impairs the ability of EphA3 to bind ephrin-A ligands in trans, we measured the binding of soluble forms of ephrin-A5 or ephrin-A3 fused to alkaline phosphatase (AP) to NCI-H226 and A549 cells expressing EphA3 alone or together with mCherry-ephrin-A3. The gene discussed is EFNA3; the disease is cancer.