Carcinoembryonic antigen (CEA; MIM 114890) is one of the most widely used tumor markers in serum immunoassay determinations of carcinoma. An apparent lack of absolute cancer specificity for CEA probably results in part from the presence in normal and neoplastic tissues of antigens that share antigenic determinants with the 180-kD form of CEA (Barnett et al., 1988 [PubMed 3220478]). For background information on the CEA family of genes, see CEACAM1 (MIM 109770).