For example, one-time screening was applied in the Cluster Randomised Trial of PSA Testing for Prostate Cancer; annual screening was undertaken in the Prostate, Lung, Colorectal and Ovarian Cancer Screening trial; and screening once every 2-4 years was performed in the European Randomised Study of Screening for Prostate Cancer [12]. This evidence concerns the gene KLK3 and prostate carcinoma.