KLK3 and prostate cancer: The best available evidence suggests that PSA screening may have a small, although uncertain, benefit on prostate cancer mortality.3 Evidence shows, however, that PSA screening also harms men because of false-positive test results and overdiagnosis and overtreatment of prostate cancer.3 Before the major prostate cancer screening trials reported their results,2,5,6 there was insufficient evidence to recommend for or against screening.