CEACAM5 and cancer: The serum biomarkers available today are based on the measurement of cancer antigens, such as prostate-specific antigen, carcinoembryonic antigen, the cancer antigens (CA15-3, CA19-9, and CA125), extracellular protein kinase A, anti-oncoprotein (HER-2/neu), anti-tumor suppression antigen (p53), anti-proliferation associated antigens (cyclin A, cyclin B1, and CDKs), anti-onconeural antigens (Hu and Yo), and anti-cancer/testis antigens (NY-ESO-1 and MAGE-1) [4,25].