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). This evidence concerns the gene KLK3 and colorectal cancer.