As an instance, prostate-specific antigen (PS-A) for prostate cancer, cancer antigen 125 (CA-125) for ovarian cancer, and carcinoembryonic antigen (CEA) and cancer antigen 19-9 (CA 19-9) for gastrointestinal cancers have long been used in cancer screening [ 67]. This evidence concerns the gene KLK3 and Familial prostate cancer.