Examples include alpha-fetoprotein (AFP) for liver cancer [149,150], cancer antigen 125 (CA125) for ovarian cancer [151,152], carcinoembryonic antigen (CEA) for colon cancer [153,154], prostate-specific antigen (PSA) for prostate cancer [155], and carbohydrate antigen 19-9 (CA19-9) for gastrointestinal and pancreatic cancers [156]. The gene discussed is KLK3; the disease is liver cancer.