Tumor markers (TMs), such as alpha fetoprotein (AFP), carcinoembryonic antigen (CEA), cancer antigen 19-9 (CA19-9) and cancer antigen 72-4 (CA72-4), have been widely used for the diagnosis of different types of cancers, including liver, colorectal cancer and pancreatic cancers. The gene discussed is CEACAM5; the disease is colorectal cancer.