In the U.K. Cluster Randomized Trial for PSA Testing for Prostate Cancer (CAP), more than 400,000 men in primary care practices between 2001 and 2009 were either invited to receive a single PSA screening test or usual care. After a median follow-up of 10 years , there were more prostate cancer diagnoses in the screening group, but no effect on prostate cancer mortality. (Men diagnosed with localized prostate cancer were invited to participate in a separate trial comparing active monitoring, surgery, and radiotherapy, which Dr. Middleton discussed previously on the AFP Community Blog.) In a secondary analysis of the CAP trial after 5 more years of follow-up, researchers found a small difference in prostate cancer mortality favoring the screening group (absolute reduction = 0.09%, number needed to screen = 1,111 to prevent one prostate cancer death). However, the screening group was at greater risk of detection of low-grade (Gleason score <=6) cancers that are likely to be clinical...