CEACAM1 and CEACAM5 belong to the carcinoembryonic antigen (CEA) gene family. It is expressed on cells of epithelial and myeloid origin. CEACAM1 expression is downregulated in many tumors indicating a tumor - suppressive function. The antitumor effect may be due to inhibition of tumor angiogenesis, possibly by increased secretion of antiangiogenic molecules from the cells. Like all members of the CEACAM family, it consists of a single N domain, with structural homology to the immunoglobulin variable domains, followed by two immunoglobulin constant-like A (A1, A2) and one B domain. While the N, A1 and B domains can also be found in other CEA-family members, the A2 domain of CEACAM1 differs from those found in other CEACAM. CEACAM5 is a cell surface glycoprotein that plays a role in cell adhesion and in intracellular signaling. CEACAM5 is a homodimer. It is a receptor for E.coli Dr adhesins. Binding of E.coli Dr adhesins leads to dissociation of the homodimer. Found in adenocarcinomas of endodermally derived digestive system epithelium and fetal colon.