There are some clinically useful tumor markers for monitoring gastric cancer, including CEA, carbohydrate antigen 19-9 in the sialyl Lewis A group (CA19-9), sialyl Tn antigen (STN), cancer antigen 72-4 (CA72-4), cancer antigen 125 (CA125), and alpha-fetoprotein (AFP) (Table 3) [46]. This evidence concerns the gene CEACAM5 and gastric cancer.