Evaluating the impact of age on prostate cancer overdiagnosis using long-term follow-up from a randomised trial

Prostate cancer overdiagnosis is detection of prostate cancer through PSA testing that otherwise would not have been diagnosed within the patient's lifetime. It is a major concern to policymakers due to its impact on quality of life. We used long-term followup data from the CAP randomised trial of a one-off screen, and English male competing mortality rates (2021-23), to estimate the impact of age on excess prostate cancer incidence within 15 years ('overdiagnosis') using competing risks methods. In total, 2249 (1.19%) of 189,386 men invited for a PSA test in CAP had cancer detected at the one-off screen. Prostate cancer cumulative incidence at 15 years was 7.08% (95%CI 6.95 to 7.21%) in those invited to screening, compared with 6.94% (95%CI 6.82 to 7.06%) in the control arm; an absolute excess incidence difference of 0.14% (95%CI -0.04% to 0.37%). Excess net incidence to 15 years was 0.14/1.19 = 11.7% (95%CI 0.0% to 26.7%) of cases detected at a single prevalent screen. Accounting for competing mortality, English men diagnosed aged 50 years were projected to have a 16% chance the cancer would not have been detected within 15 years, rising to 32% aged 70 years and 58% aged 80 years. Thus, prostate cancer overdiagnosis rises substantially with age due to competing mortality, and is relatively low for younger men. Accordingly, opportunistic testing policies should be re-examined in settings where they have led to high rates of screening in older men.