Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) also known as CD66e (Cluster of Differentiation 66e), is a member of the carcinoembryonic antigen (CEA) gene family. In the literature, CEACAM5 is often used as a synonym for cancer embryonic antigen (CEA), a well-known biomarker of many types of malignancies, colorectal cancer in the first place. Its primary function in the embryonic intestine and colon tumors is adhesion between epithelial cells. Also, it plays a significant role in the inhibition of differentiation and apoptosis in colon cells. There are evidences that high CEACAM5 expression is firmly associated with the CD133-positive colorectal cancer stem cells.