Biomarkers for diagnosis and prognosis of gastric cancer that have previously been identified are mostly non tumor tissue based, and include carcinoembryonic antigen (CEA), CA 125, CA 19–9, CA 72–4 and alpha-fetoprotein [6, 8], serum pepsinogen I, and proteases (pepsinogen C, plasminogen activator, matrix metalloproteinases and their inhibitors) [9]. Here, CEACAM5 is linked to gastric cancer.