Carcinoembryonic antigen (CEA) also known as Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5), CD antigen CD66e, Meconium antigen 100, is an oncofetal glycoprotein that is normally expressed by mucosal cells. CEA is a member of the immunoglobulin (Ig) superfamily of proteins. CEA is a glycophosphatidylinositol- (GPI-) linked membrane-anchoring protein that is exposed to the cell surface that faces the extracellular matrix. The membrane-anchoring region of CEA can be cleaved by phospholipase C and phospholipase D. The cleaved products are soluble and circulating through blood vessels. Thus, CEA can be present as secreted and cell surface-anchored forms. CEA is functionally associated with cellular interaction, cell adhesion, immune response, anoikis resistance, and promotion of liver metastasis. CEA overexpression is associated with many types of cancers including gastrointestinal, respiratory, and genitourinary system and breast cancers.