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

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. Cellbound CEA has served as a target for tumor imaging and various cancer therapies.