The number of cases of prostate cancer (PCa) has increased globally by 40% in 10 years, from 1.4 million in 2016 to 1.0 million in 2006.[1] This increase has been associated with the introduction of Prostate Specific Antigen (PSA) testing in the 1990s, with the variation observed between countries explained by differences in use of PSA tests.[2–4]. This evidence concerns the gene KLK3 and prostate cancer.