Evidence from the European Randomized Study of Screening for Prostate Cancer suggests that when PSA testing is offered to all men, it reduces prostate cancer mortality by approximately 28% at 13 years of follow-up.37 If we assume that the use of PSA testing is 20% among men who have not had a vasectomy and 40% among men who have (data from EPIC-Oxford), it is possible that increased screening in the latter could result in a 5.6% reduced risk of death due to prostate cancer. This evidence concerns the gene KLK3 and prostate cancer.