Carcinoembryonic antigen (CEA) is a glycoprotein, which was first identified in patients with colon carcinoma and in epithelial tumors of endodermal origin (gastrointestinal tract) by Gold and Freedman. The CEA molecule is quite heterogeneous due to the carbohydrate contents (50%-60%) and depending on the purification procedure employed. It is soluble in perchloric acid and has a molecular weight of about 175.000 to 200.000 Daltons. Immunological and genetic characterization of CEA has identified a family of CEA-like molecules sharing common antigenic determinants. The most relevant CEA-like molecule is NCA (nonspecific cross-reacting antigen) synthesized both by normal and pathological tissues. The problem of cross-reacting CEA-like molecules when assaying CEA is possible to overcome by the use of monoclonal antibodies. The CEA EIA is based on two mouse monoclonal antibodies against the Gold epitopes IV and V.

CEA is secreted from tumor cells and is a widely used serological marker of gastrointestinal carcinomas, lung cancer, and breast cancer. In colorectal cancer, the clinical use of CEA testing for monitoring response to therapy and for documenting progressive disease is well established. CEA may also be present in benign gastrointestinal inflammatory diseases or in hepatobiliary diseases. These observations make it necessary to emphasize that the CEA assay should not be used as a cancer-screening test.