Several main tumor markers have been extensively analyzed for the diagnosis of hepatocellular carcinoma, epithelial ovarian tumors, pancreatic cancer, colorectal cancer, and others, including human chorionic gonadotropin (hCG), prostate specific antigen (PSA), alphafetoprotein (AFP), carcinoma antigen 125 (CA125), carbohydrate antigen (CA19-9, CA15-3), and carcinoembryonic antigen (CEA). The gene discussed is AFP; the disease is colorectal cancer.