Although the clinical introduction of the Prostate-Specific Antigen (PSA) test in 1986 increased the early diagnosis of localized prostate cancer (Catalona et al., 1991; Hankey et al., 1999), elevated PSA levels are not necessarily indicative of prostate cancer because PSA levels can be raised by prostatitis, other localised infections, benign hyperplasia and/or factors such as physical stress. This evidence concerns the gene KLK3 and prostate cancer.