Recombinant human carcinoembryonic antigen (CEA) CEACAM5, also known as CEA or CD66e, belongs to the large CEACMA subfamily of the immunoglobulin superfamily. CEACAM5 is mainly expressed by epithelial cells and is a glycoprotein with a molecular weight of 180 kDa and containing 60% carbohydrates. At the N-terminal of CEACAM5, there is an immunoglobulin V-type domain, followed by six immunoglobulin C2-type domains and a glycosylphosphatidylinositol anchor (also known as a point), which exists in the form of homologous dimers. CEACAM5 and CEACAM6 are overexpressed in many tumor tissues and are associated with tissue adhesion and invasion. It acts as a homotypic intercellular adhesion molecule and is a widely used tumor marker because it has a higher expression level in tumor tissue compared to corresponding normal tissues.