Carcinoembryonic antigen (CEA) was first described in 1965 by Gold and Freedman when they identified an antigen that was present in both fetal colon and colon adenocarcinoma but that appeared to be absent from healthy adult colon. CEA is a glycoprotein containing approximately 50% carbohydrate with a molecular weight of 180 kDa. CEA and related genes make up the CEA family belonging to the immunoglobulin superfamily. In humans, the carcinoembryonic antigen family consists of 29 genes, 18 of which are normally expressed. CEA has proven to be a suitable target antigen for the detection of primary and metastatic colorectal and some other carcinomas. Although sera from healthy individuals and from patients with other diseases generally had low levels of CEA, CEA is one of the most widely used tumor markers worldwide. Its main application is mostly in gastrointestinal cancers, especially in colorectal malignancy. CEA assays are now generally accepted clinically as a useful and cost-efficient tool in monitoring of colon cancer following surgery. Cell surface glycoprotein that plays a role in cell adhesion and in intracellular signaling. Receptor for E.coli Dr adhesins.