CEACAM5, also known as carcinoembryonic antigen (CEA) or CD66e, is a member of the immunoglobulin superfamily, mainly serving as a cell adhesion molecule mediating intercellular contact by both homophilic and heterophilic binding. CEACAM5 is overexpressed in a wide variety of human cancers, including colon, breast, and lung. It inhibits anoikis and plays a role in tumorigenesis and metastasis. CEACAM5 is not usually present in the blood of healthy adults. However, it has been found that serum from people with colorectal, gastric, pancreatic, lung, and breast carcinoma has higher levels of CEACAM5 than healthy people. CEACAM5 is a tumor marker and is routinely exploited for diagnosis.