Number of Screening Rounds and Postscreening Prostate Cancer Incidence: Results from the Finnish Section of the European Randomized Study of Screening for Prostate Cancer Study

BackgroundThe multicenter European Randomized Study of Screening for Prostate Cancer has shown a 21% reduction in prostate cancer (PC) mortality by prostate-specific antigen-based screening, with substantial overdiagnosis. In the present study, we analyzed the incidence of PC after screening in relation to the number of screening rounds attended in the Finnish section of the trial.ObjectiveTo evaluate the possible reduction in PC incidence following completed screening cycles in relation to the number of screening rounds attended.Design, setting, and participantsThe participants in the screening arm of the Finnish screening trial (29 298 men) were divided into subgroups of men who had participated at one, two, or three screening rounds. A reference group was formed of the 43 151 men in the control arm by selecting age-matched controls for each subgroup of the screening participants. PC cases diagnosed after screening were identified from the Finnish Cancer Registry until the end of 2011. Follow-up of the screened men started 12 mo (365 d) after the last screening attendance and a similar date was assigned to the men in the control arm.Results and limitationsA total of 1514 new PCs cases (cumulative incidence 5.2%) were diagnosed among the screened men after the last screening attendance. In the reference group formed from the control arm, 2683 cases (6.2%) occurred. The hazard ratio (HR) for PC among nonparticipants in the screening arm was 0.89 (95% confidence interval [CI] 0.79-0.99) compared with their controls. Among participants, the HR in those who participated once was 1.39 (95% CI 1.22-1.57), among men who participated twice the HR was 0.97 (95% CI 0.86-1.10), and among men screened three times the HR was 0.57 (95% CI 0.49-0.68). A limitation of the study was that the comparison by attendance is not based on randomization.ConclusionsThe postscreening PC incidence is reduced after attending three screening rounds, but not after only one or two rounds. Thus, the increased cancer detection at screening is compensated by a subsequent risk reduction only after repeated screening cycles.Patient summaryThe results of the study indicate that at least three prostate-specific antigen-based screening cycles are needed to reduce subsequent prostate cancer incidence.