In 36 studies, prostate cancer was confirmed by a histopathological examination [19, 20, 22, 24, 26, 57–59, 61–64, 67–69, 71–74, 76–78, 80, 82–89, 92, 97, 100–102]; in two studies it was confirmed by prostate-specific antigen (PSA) test [81, 94], and in one study it was confirmed by clinical data and current international clinical staging method [93]. Here, KLK3 is linked to prostate cancer.