CEA-related cell adhesion molecules (CEACAM) belong to the carcinoembryonic antigen (CEA) family. It consists of seven CEACAM (CEACAM 1，CEACAM 3-CEACAM 8) and 11 pregnancy-specific glyco-protein (PSG 1-PSG 11) members. The CEA family proteins belong to the immunoglobulin (Ig) superfamily and are composed of one Ig variable-like (IgV) and a varying number (0-6) of Ig constant-like (IgC) domains. CEACAM molecules are membrane-bound either via a transmembrane domain or a glycosyl phosphatidyl inositol (GPI) anchor. CEACAM molecules are differentially expressed in epithelial cells or in leucocytes. Over-expression of CEA/ CEACAM 5 in tumors of epithelial origin is the basis of its wide-spread use as a tumor marker. The function of CEACAM family members varies widely: they function as cell adhesion molecules，tumor suppressors，regulators of lymphocyte and dendritic cell activation，receptors of Neisseria species and other bacteria.