Comparison of the Swedish and Finnish Centers in the European Randomized Study of Screening for Prostate Cancer (ERSPC)

The Finnish and Swedish parts of the European Randomized Study of Screening for Prostate Cancer trial reported marked difference in prostate cancer mortality effects after 16 year. Extensive contamination of the Finnish control group from the study’s start may explain the smaller mortality reduction in FinRSPC. The European Randomized Study of Screening for Prostate Cancer showed 20% reduction in prostate cancer (PC) mortality after 16 year follow-up of prostate-specific antigen (PSA) based screening, but effects varied: 9% in Finland (FinRSPC) vs 37% in Sweden (Göteborg-1) in screening vs control groups. The objective was to explore this difference. The data comprised 64 774 participants in FinRSPC and 10 703 men in Göteborg-1, aged 55–63 year at randomization (FinRSPC: 1996–1999; Göteborg-1: 1995). Screening invitations were issued for PSA testing every 4 year, with biopsy recommended if PSA ≥4 ng/ml, or 3–3.99 ng/ml with an additional test in FinRSPC; and every 2 year, with biopsy recommended at PSA ≥3 ng/ml in Göteborg-1. Expected incidence/mortality was based on registry data (1990–1994, and 2010–2014). Outcomes included cumulative PC incidence, PC-specific mortality, and relative risks. In Göteborg-1, PC incidence was 44% higher (95% CI confidence interval: 29–61) and PC mortality 36% lower (95% CI: 7–56) in screening vs control groups. In FinRSPC, PC incidence was 21% higher (95% CI: 15–27) and PC mortality 2% lower (95% CI: –19–19). Screening groups in both centers had approximately 40% lower mortality than expected with 1990–1994 rates, similar to 2010–2014 rates. Swedish controls resembled expected rates in 1990–1994 and Finnish controls in 2010–2014. A key limitation was the exploratory nature of the study. The lower effect on PC mortality in FinRSPC appears attributable to unexpectedly low mortality in the control group, possibly due to extensive contamination from the start of the study. Findings highlight the challenges in demonstrating mortality benefit in screening trials under widespread opportunistic testing.