In an effort to increase the chances of detecting cancer earlier, non-invasive screening tests have been introduced into clinical practice, such as: a) carcinoembryonic antigen (CEA)9, mainly used for monitoring of cholangiocarcinoma, b) cancer antigen 125 (CA-125)10 primarily used to monitor treatment of ovarian cancer, c) prostate specific antigen (PSA)11 used for the detection of prostate cancer and d) carbohydrate antigen 19-9 (CA19-9)12 mainly applied for the detection of pancreatic cancer. The gene discussed is KLK3; the disease is prostate cancer.