For example, the FDA approved cancer biomarkers based on serum level of O-glycosylated mucin glycoproteins of carbohydrate antigens (CA125 for ovarian, CA27.29 and CA15-3 for breast, CA19-9 for pancreatic cancers) and N-glycosylated glycoproteins (α-fetoprotein for hepatocellular carcinoma, prostate-specific antigen for prostate cancer) lack the specificity and sensitivity to be used for early detection of cancer [16, 17]. This evidence concerns the gene KLK3 and cancer.