MEDI-565 binds to mature full-length CEA. However, polymorphisms and/or isoforms of CEA may alter the binding epitope and negatively affect the ability of MEDI-565 to bind. Once the epitope of CEA bound by MEDI-565 had been identified, the ability of MEDI-565 to recognize cancerous cells expressing polymorphisms and isoforms of CEA could be evaluated.