CEACAM5 (carcinoembryonic antigen-related cell adhesion molecule 5 (carcinoembryonic antigen))

2015-08-01   Naoto Shirasu , Masahide Kuroki 


Atlas Image
A schematic representation of the chromosomal arrangement of the CEACAM family genes. Main members (CEACAM1, CEACAM3, CEACAM4, CEACAM5, CEACAM6 CEACAM7 and CEACAM8) of the CEACAM family are localized in the region of the chromosome 19q13.2.


The CEACAM5 gene encodes carcinoembryonic antigen (CEA), which was first identified as an oncofetal antigen in 1965 in human colon cancer tissue extracts. CEA is a heavily glycosylated protein that belongs to the CEA-related cell adhesion molecule (CEACAM) family of the immunoglobulin (Ig) gene superfamily. CEA is closely related to CEACAM1, CEACAM3, CEACAM4, CEACAM5, CEACAM6, CEACAM7, and CEACAM8. CEA is also expressed at low levels in normal tissues of epithelial origin in a polarized manner and found only at the luminal portion of the cell, but not at the basolateral surface. CEA in normal tissues is now considered to protect the luminal organs of the body from microbial infection by binding and trapping infectious microorganisms. In contrast, the expression of CEA is frequently high in various carcinomas. Cancer cells not only lose polarized expression of CEA, but also actively cleave CEA from their surface by phospholipases, resulting in increased serum concentrations of CEA. The serum CEA levels may be monitored to detect a response to cancer therapy or disease recurrence and serve as a prognostic indicator in patients with various cancers, where elevated levels indicate a poor prognosis and correlate with a reduced overall survival. Cell-bound CEA has served as a target for tumor imaging and various cancer therapies.



Out of 24 CEACAM family genes, twelve members (i.e., CEACAM1, CEACAM3, CEACAM4, CEACAM5, CEACAM6, CEACAM7, CEACAM8, CEACAM16, CEACAM18, CEACAM19, CEACAM20 and CEACAM21) are expressed while the other 12 genes are pseudogenes (Pavlopoulou and Scorilas, 2014). All the CEACAM family genes are localized in the 19q13.2-19q13.4 region. Although the newly given protein names encoded by those active genes are the same as the gene names (Beauchemin et al., 1999), that of CEACAM5 is still CEA because the name of CEA has clinically been widely used for a long time. Splice variants isoforms of CEACAM/CEA have been detected, and the resulting protein isoforms were not only co-expressed with full-length CEA but also co-secreted into the culture medium by gastrointestinal cancer cell lines (Hatakeyama et al., 2013).
Atlas Image
(A) Alternative splicing of CEA precursor mRNA leads to the shorter isoforms with different domain structures. Protein-coding exons (exons 1-9) are shown as yellow boxes; the 3-untranslated exon 10, the light yellow box. (B) Schematic representations of the protein domain structures of the translated CEA transcripts. The black sigmoidal line attached to the B3 IgC-like domain indicates a glycosylphosphatidylinositol (GPI) anchor to the plasma membrane (see below).


The CEACAM5 gene, spanning a length of approximately 21 kb, consists of 9 exons with a 3-non-coding exon (exon 10).


The primary CEA transcript encodes a protein with an Ig variable region (IgV)-like domain, termed N, followed by six Ig constant region (IgC)-type 2-like domains, termed A1, B1, A2, B2, A3, and B3. In some normal and cancer cells, the transcript is subjected to alternative splicing, resulting in the generation of several CEA isoforms (Hatakeyama et al., 2013). The CEA transcript with skipping of exons 3-4 encodes the variant with a five-domain structure (N-A2-B2-A3-B3 (5D)), while the transcript lacking the sequence from the 3 end of exon 3 to the 5 end of exon 7 relative to the full-length transcript contains only three domains (N-A1-B3 (3D)).


Out of 24 CEACAM family genes, twelve are pseudogenes and have been identified in the CEA family gene cluster (Pavlopoulou and Scorilas, 2014).



The CEACAM5 gene encodes CEA, which is the most widely used tumor marker for the diagnosis and monitoring of various cancers (see below). CEA is composed of 642 amino acids (a molecular mass of approximately 70kDa) and has 28 potential N-linked glycosylation sites (Oikawa et al., 1987; Nicholson and Stanners, 2007). CEA contains 24-26 asparagine-linked sugar chains in one molecule (Yamashita et al., 1987) and its final molecular mass is approximately 180kDa (Thompson et al., 1991).
Atlas Image
(A) The gene structure and protein domain model of the CEA molecule. CEA encoded by the CEACAM5 gene is synthesized as a precursor with a signal peptide (S) followed by 668 amino acids of the putative molecule; the first N-terminal domain (N domain) is followed by six IgC-like domains (A1, B1, A2, B2, A3, and B3 domains) and the last C-terminal hydrophobic domain (C domain) (Oikawa et al., 1987). Exons 1 and 9 include a 5-untranslated region (5-UTR) and a 3-untranslated region (3-UTR), respectively (Schrewe et al., 1990). (B) Schematic representation of the CEA protein structure. CEA is finally anchored to the membrane by the simultaneously occurring proteolysis of the C domain and replacement with the GPI anchor immediately after synthesis (Takami et al., 1988).


Among the main CEACAM family members (CEACAM1, CEACAM3, CEACAM4, CEACAM5, CEACAM6 CEACAM7 and CEACAM8), the genes encoding proteins with transmembrane domains were assigned the CEACAM consecutive numbers 1-4, and the genes encoding GPI-anchored proteins including CEA were assigned the CEACAM numbers 5-8 (Beauchemin et al., 1999).


Many CEACAM family proteins, such as CEACAM1, CEACAM8, CEACAM6 and CEACAM3, are known to be expressed in hematopoietic cells (Nagel and Grunert, 1995; Baeclay et al., 1997). In contrast, CEA has not been detected in hematopoietic cells and shows a more limited tissue localization in normal tissues including the tongue, esophagus, stomach, duodenum, appendix, colon, trachea (Nap et al., 1988; Kuroki et al., 1981) and lung (Nouwen et al., 1986). The CEA expression in those organs starts during the early fetal period (9-14 weeks) and appears to continue throughout ones lifespan (Nap et al., 1988). Increased expression of CEA has also been observed in various cancers including colorectal carcinoma (Jothy et al., 1993), gastric carcinoma (Kinugasa et al., 1998), pancreatic carcinoma (Shi et al., 1994), gall bladder carcinoma (Shi et al., 1994), lung adenocarcinoma (Robbins et al., 1993), small cell lung carcinoma (Kim et al., 1992), breast carcinoma (Cournoyer et al., 1988), urinary bladder carcinoma (Shi et al., 1994), mucinous ovarian carcinoma (Thompson et al., 1994), serous ovarian carcinoma (Thompson et al., 1993) and endometrial adenocarcinoma (Thompson et al., 1993). It is usually expressed in corresponding metastatic lesions as well, due to its involvement in tumor progression and metastasis.


CEA is localized to columnar epithelial cells and goblet cells of the colon, mucous neck cells and pyloric mucous cells of the stomach, squamous epithelial cells of the tongue, esophagus and cervix, secretory epithelia and duct cells of sweat glands and epithelial cells of the prostate (Nap et al., 1988; Kodera et al., 1993; Prall et al., 1996). Studies using immunoelectron microscopy using a specific monoclonal antibody for CEA demonstrate that CEA is specifically localized to the apical surface of mature enterocytes (Ahnen et al., 1982; Baranov et al., 1994; Frãngsmyr et al., 1999). No staining is seen at the basolateral surfaces of the enterocytes. The structure that is specifically stained is the apical glycocalyx (= fuzzy coat)/microvillus region of the mature enterocytes. The fuzzy coat is made up of microvesicles and filaments. The microvesicles are formed by the blebbing of microvillus membrane and subsequent pinching off. The finding that CEA in normal colon is released via CEA-coated vesicles agrees with the findings which showed that more than 90% of total CEA in feces exist in a membrane-bound form and that it can be released from the membranes by phosphatidylinositol-specific phospholipase C (Kuroki et al., 1994; Kinugasa et al., 1994).


In vitro studies with tumor cell lines have demonstrated that CEA, like other CEA gene family members, can act as homophilic and heterophilic adhesion molecules when expressed on the tumor cell surface (Benchimol et al., 1989; Oikawa et al., 1992; Zhou et al., 1993). Therefore, in the tumor environment it is possible that CEA plays some role as a contact-mediating device when tumor cells are invading new sites. In normal physiology, however, it appears unlikely that CEA is involved in intercellular adhesion due to their apical localization on polarized cells. CEA in normal tissues is now considered to protect the luminal organs of the body from microbial infection by binding and trapping infectious microorganisms. Those organs are the colon and perhaps other areas, such as the upper alimentary tract, the respiratory tract, the urinary bladder, and the skin (sweat glands), where the microbial load is a routine event (Hammarström, 1999).


The CEACAM5 gene homologue is present in primates such as chimpazees, orangutans, macaques and marmosets, but not in rodents such as mice and rats (Pavlopoulou and Scorilas, 2014).



As of July 2015, the 245 single-nucleotide polymorphisms (SNPs) of the CEACAM gene have been included in the NCBI SNP database (dbSNP), and there are 19 independent SNPs located within the coding region.  However, to date, no clinical significance of these CEACAM SNPs has been described.

Implicated in

Entity name
Various cancers
As described above, CEA is widely expressed not only on the surface of tumor cells, but also on normal epithelial cells of the luminal organs of the body. These facts demonstrate that CEA is no longer a carcinoembryonic (oncofetal) antigen, rather it should be considered to be a normal tissue component with retained/increased expression in tumors (Kuroki et al., 1988; Hammarström, 1999). The degree of its expression is related to the state of differentiation of the normal or tumor cell; highly differentiated cells express higher levels of CEA (Hammarström, 1999). The localization of CEA in normal adult tissues is, however, restricted to the apical surface of the epithelial cell membranes facing the lumen, so that CEA is not directly exposed to the tissue fluid or blood flow. In contrast, in tumor tissues that no longer conform to the single-layer organization by invading through the basement membrane in multicellular arrays, CEA is typically localized to all sides of the cell surface, directly facing the blood flow or tissue fluid (Hammarström, 1999; Khare et al., 2001). As the tumor size increases, more CEA will accumulate in the blood. Hence, the serum CEA levels may be monitored to detect a response to anticancer therapy or disease recurrence in various cancers, especially in colorectal cancer (Goldstein Mitchell, 2005; Locker et al., 2006). Immunohistochemical staining of CEA using surgically- or biopsy-removed specimens is also helpful as a diagnostic aid in patients with various cancers (Kuroki et al., 2002).
Serum CEA serves as a prognostic indicator in patients with various types of cancer, where elevated levels indicate a poor prognosis and correlate with a reduced overall survival (Duffy, 2001; Locker et al., 2006).


Pubmed IDLast YearTitleAuthors
70420661982Ultrastructural localization of carcinoembryonic antigen in normal intestine and colon cancer: abnormal distribution of CEA on the surfaces of colon cancer cells.Ahnen DJ et al
209243622011Bispecific adapter-mediated retargeting of a receptor-restricted HSV-1 vector to CEA-bearing tumor cells.Baek H et al
82055541994Expression of carcinoembryonic antigen and nonspecific cross-reacting 50-kDa antigen in human normal and cancerous colon mucosa: comparative ultrastructural study with monoclonal antibodies.Baranov V et al
115015631999Redefined nomenclature for members of the carcinoembryonic antigen family.Beauchemin N et al
27026911989Carcinoembryonic antigen, a human tumor marker, functions as an intercellular adhesion molecule.Benchimol S et al
28351541988Transcription of genes of the carcinoembryonic antigen family in malignant and nonmalignant human tissues.Cournoyer D et al
112740102001Carcinoembryonic antigen as a marker for colorectal cancer: is it clinically useful?Duffy MJ et al
104364211999Four carcinoembryonic antigen subfamily members, CEA, NCA, BGP and CGM2, selectively expressed in the normal human colonic epithelium, are integral components of the fuzzy coat.Frängsmyr L et al
161009462005Carcinoembryonic antigen in the staging and follow-up of patients with colorectal cancer.Goldstein MJ et al
102021291999The carcinoembryonic antigen (CEA) family: structures, suggested functions and expression in normal and malignant tissues.Hammarström S et al
240701902013Novel protein isoforms of carcinoembryonic antigen are secreted from pancreatic, gastric and colorectal cancer cells.Hatakeyama K et al
195785242008Radionuclide-Based Cancer Imaging Targeting the Carcinoembryonic Antigen.Hong H et al
111961892001Specifically targeted killing of carcinoembryonic antigen (CEA)-expressing cells by a retroviral vector displaying single-chain variable fragmented antibody to CEA and carrying the gene for inducible nitric oxide synthase.Khare PD et al
13309291992Expression of carcinoembryonic antigen and related genes in lung and gastrointestinal cancers.Kim J et al
95337751998Expression of four CEA family antigens (CEA, NCA, BGP and CGM2) in normal and cancerous gastric epithelial cells: up-regulation of BGP and CGM2 in carcinomas.Kinugasa T et al
83184031993Expression of carcinoembryonic antigen (CEA) and nonspecific crossreacting antigen (NCA) in gastrointestinal cancer; the correlation with degree of differentiation.Kodera Y et al
32033251988Active production and membrane anchoring of carcinoembryonic antigen observed in normal colon mucosa.Kuroki M et al
61609101981Purification and characterization of carcinoembryonic antigen-related antigens in normal adult feces.Kuroki M et al
81907121994Fractionation of carcinoembryonic antigen and related antigens in normal adult feces using a gradient medium Percoll.Kuroki M et al
250750902014Novel treatment strategies for cancer and their tumor-targeting approaches using antibodies against tumor-associated antigens.Kuroki M et al
125530662002Significance of tumor-associated antigens in the diagnosis and therapy of cancer: an overview.Kuroki M et al
170606762006ASCO 2006 update of recommendations for the use of tumor markers in gastrointestinal cancer.Locker GY et al
264055112015Role of cytokines in Trypanosoma brucei-induced anaemia: A review of the literature.Musaya J et al
78632181995From genes to proteins: the nonspecific cross-reacting antigens.Nagel G et al
33998131988Immunohistochemistry of carcino-embryonic antigen in the embryo, fetus and adult.Nap M et al
35100761986Immunohistochemical localization of placental alkaline phosphatase, carcinoembryonic antigen, and cancer antigen 125 in normal and neoplastic human lung.Nouwen EJ et al
14976721992Homotypic and heterotypic Ca(++)-independent cell adhesion activities of biliary glycoprotein, a member of carcinoembryonic antigen family, expressed on CHO cell surface.Oikawa S et al
38141461987Primary structure of human carcinoembryonic antigen (CEA) deduced from cDNA sequence.Oikawa S et al
248584212014A comprehensive phylogenetic and structural analysis of the carcinoembryonic antigen (CEA) gene family.Pavlopoulou A et al
225741572012The CEA/CD3-bispecific antibody MEDI-565 (MT111) binds a nonlinear epitope in the full-length but not a short splice variant of CEA.Peng L et al
85437801996CD66a (BGP), an adhesion molecule of the carcinoembryonic antigen family, is expressed in epithelium, endothelium, and myeloid cells in a wide range of normal human tissues.Prall F et al
83861361993Definition of the expression of the human carcinoembryonic antigen and non-specific cross-reacting antigen in human breast and lung carcinomas.Robbins PF et al
23424611990Cloning of the complete gene for carcinoembryonic antigen: analysis of its promoter indicates a region conveying cell type-specific expression.Schrewe H et al
75204631994Monoclonal antibody COL-1 reacts with restricted epitopes on carcinoembryonic antigen: an immunohistochemical study.Shi ZR et al
247402572014Potent and specific antitumor effect of CEA-targeted photoimmunotherapy.Shirasu N et al
264108602016Acute and long-term effects of hyperbaric oxygen therapy on hemorheological parameters in patients with various disorders.Sinan M et al
28423401988Evidence for carboxyl-terminal processing and glycolipid-anchoring of human carcinoembryonic antigen.Takami N et al
167781082006Carcinoembryonic antigen-targeted selective gene therapy for gastric cancer through FZ33 fiber-modified adenovirus vectors.Tanaka T et al
78065201994CGM2, a member of the carcinoembryonic antigen gene family is down-regulated in colorectal carcinomas.Thompson J et al
19413551991Carcinoembryonic antigen gene family: molecular biology and clinical perspectives.Thompson JA et al
35810811987Structural studies of the carbohydrate moieties of carcinoembryonic antigens.Yamashita K et al
76879261993Specificity of anti-carcinoembryonic antigen monoclonal antibodies and their effects on CEA-mediated adhesion.Zhou H et al

Other Information

Locus ID:

NCBI: 1048
MIM: 114890
HGNC: 1817
Ensembl: ENSG00000105388


dbSNP: 1048
ClinVar: 1048
TCGA: ENSG00000105388


Gene IDTranscript IDUniprot

Expression (GTEx)



PathwaySourceExternal ID
Metabolism of proteinsREACTOMER-HSA-392499
Post-translational protein modificationREACTOMER-HSA-597592
Post-translational modification: synthesis of GPI-anchored proteinsREACTOMER-HSA-163125
Cell surface interactions at the vascular wallREACTOMER-HSA-202733

Protein levels (Protein atlas)

Not detected


Pubmed IDYearTitleCitations
183753922008Carcinoembryonic antigen and CD44 variant isoforms cooperate to mediate colon carcinoma cell adhesion to E- and L-selectin in shear flow.66
172019062007Expression patterns of CEACAM5 and CEACAM6 in primary and metastatic cancers.62
233520322013Diagnostic value of CEA and CYFRA 21-1 tumor markers in primary lung cancer.52
277487682016Helicobacter pylori adhesin HopQ engages in a virulence-enhancing interaction with human CEACAMs.52
286603192017The clinical efficacy of first-generation carcinoembryonic antigen (CEACAM5)-specific CAR T cells is limited by poor persistence and transient pre-conditioning-dependent respiratory toxicity.44
193860892009Brain metastasis development and poor survival associated with carcinoembryonic antigen (CEA) level in advanced non-small cell lung cancer: a prospective analysis.42
277487562016Helicobacter pylori exploits human CEACAMs via HopQ for adherence and translocation of CagA.42
151301182004Differential recognition of members of the carcinoembryonic antigen family by Afa/Dr adhesins of diffusely adhering Escherichia coli (Afa/Dr DAEC).41
208139532010Human-restricted bacterial pathogens block shedding of epithelial cells by stimulating integrin activation.38
159055092005Carcinoembryonic antigen (CEA) inhibits NK killing via interaction with CEA-related cell adhesion molecule 1.36


Naoto Shirasu ; Masahide Kuroki

CEACAM5 (carcinoembryonic antigen-related cell adhesion molecule 5 (carcinoembryonic antigen))

Atlas Genet Cytogenet Oncol Haematol. 2015-08-01

Online version: http://atlasgeneticsoncology.org/gene/40047/ceacam5