Mean lead times and sojourn times due to PSA screening have been estimated in retrospective studies that used stored blood samples obtained from individuals who were later clinically diagnosed with prostate cancer (Stenman et al, 1994; Auvinen et al, 2002) and in simulation studies (Draisma et al, 2003; Telesca et al, 2008). This evidence concerns the gene KLK3 and prostate cancer.