The Number of Screening Cycles Needed to Reduce Prostate Cancer Mortality in the Finnish Section of the European Randomized Study of Prostate Cancer (ERSPC)

Purpose: The European Randomized Study of Screening for Prostate Cancer (ERSPC) has shown a 21% reduction in prostate cancer (PC) mortality by PSA-based screening. The aim of the study is to evaluate screening effect on PC incidence and mortality in relation to number of screening rounds attended. Experimental Design: The participants of the Finnish ERSPC trial (31,867 men) were classified according to screening attendance. All men were regarded as non-attenders until the first screening attendance, then remained once-screened until the second screen and similarly for the third round. The control arm was the reference. Follow-up started at randomization and ended at death, emigration or end of 2013. PC incidence and mortality, lung cancer and overall mortality were evaluated. Results: PC mortality was decreased in men screened twice or three times, but did not materially differ in those who did not attend the screening and in men screened once compared with the control arm. The largest mortality reduction was in men screened three times (HR:0.17, 95% CI:0.09-0.33). However, a reduction was also seen in lung cancer (HR:0.59, 95% CI:0.47-0.73) and overall mortality (HR:0.56, 95% CI:0.52-0.60). Conclusions: Assuming a similar relative reduction being due to selection bias and screening in PC as other causes of death (40% reduction), approximately half of the observed PC mortality reduction by repeated screening is likely to be non-causal and a real screening effect may account for up to 40% reduction in men screened three times. PC mortality reduction can only be achieved by repeated screening cycles.

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