CEACAM5 and colorectal cancer: Among them, carcinoembryonic antigen (CEA), a set of glycoproteins highly relevant to cell adhesion, has been considered as a commonly used cancer biomarker in clinical diagnosis, because its overexpression in human blood serum often means the presence or progression of various diseases such as colorectal cancer, pancreatic cancer, and lung carcinoma [4,5,6,7].