The Cluster randomised triAl of PSA testing for Prostate cancer (CAP) is an effectiveness trial comparing PCa-specific mortality in men invited (intervention arm) and men not invited (control arm) to prostate-specific antigen (PSA) testing in primary care [5] and the Prostate testing for cancer and treatment (ProtecT) randomised controlled trial (RCT), which evaluates the effectiveness and cost-effectiveness of treatment for localised, PSA-detected PCa [6]. Here, KLK3 is linked to cancer.