Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5), also known as CD66e, belongs to the large family of CEACAM and pregnancy specific glycoproteins. It is expressed primarily by epithelial cells, consists of an N-terminal Ig like V-type domain followed by six Ig-like C2-type domains and a GPI anchor. CEACAM5 is restricted to the apical face of intestinal epithelial cells in the adult but is more diffuse during embryonic development and in tumors. CEACAM5 is upregulated in a wide variety of human tumors and is a commonly used cancer marker. It promotes tumor cell migration, invasion, adhesion, and metastasis. CEACAM5 also contributes to tumor formation by maintaining cellular proliferation in the presence of differentiation stimuli. In addition, CEACAM5 is identified as the host receptor for the Dr family of adhesins of E.Coli, and the binding of E.coli Dr adhesins leads to dissociation of the CEACAM5 homodimer.