It recognizes a glycoprotein of 180kDa, identified as carcinoembryonic antigen (CEA or CD66e), which is synthesized during development in the fetal gut and is re-expressed in increased amounts in intestinal carcinomas and several other tumors. This antibody has a high affinity for CEA and shows no detectable reactivity for CEA-related antigens, such as nonspecific cross-reacting antigen (NCA) and biliary glycoprotein (BGP). It shows no cross-reaction with human polymorphonuclear leucocytes. This antibody shows no reaction with a variety of normal tissues and is superb for staining of formalin/paraffin tissues. CEA is not found in benign glands, stroma, or malignant prostatic cells. Antibody to CEA is useful in detecting early foci of gastric carcinoma and in distinguishing pulmonary adenocarcinomas (60-70% are CEA+) from pleural mesotheliomas (rarely or weakly CEA+).