Thirty years of breast cancer screening and socioeconomic inequalities: A national register-based study in Finland

Background : The national wide Finnish breast cancer screening program has operated since 1992, yet the long-term effects of screening and socioeconomic inequalities remain incompletely characterized. This study examines 30 years of screening invitations, participation, diagnostic stage, and mortality, with a focus on educational disparities. Methods: We used data from the Mass Screening Registry, which contains more than 8 million screening invitations issued to 1.2 million women aged 50-69 during 1992-2022. These data were linked with demographic information from Statistics Finland and cancer diagnosis records from the Finnish Cancer Registry. All invited individuals and participation were stratified by education. Survival differences by educational level and screening participation status were assessed using Kaplan-Meier survival curves. Overall mortality was analyzed using Cox proportional hazards models adjusted for education, marital status, urbanization level of residence, and stage at diagnosis. Effects of screening and education on early-stage detection (stage I-II vs. III-IV) were assessed using logistic regression models. Results: Screening participation displayed a clear socioeconomic gradient (low education 80.2%, medium 84.7%, high 85.7%) and slightly decreased by year. Mean age at death was higher among screened than unscreened women overall (+2.65 years, 81.73 vs. 79.08), and the survival advantage was largest in the lower-educated group (+3.51 years, 81.12 vs. 77.61) than in the higher-educated group (+1.56 years, 82.38 vs. 80.82). Screening participation was associated with a 54% reduction in mortality (HR = 0.46, 95% CI 0.45-0.46) after full adjustment. Screened women had more than double the odds of early-stage diagnosis (OR = 2.31, 95% CI 2.00-2.68). Higher-educated women were more likely to receive an early-stage diagnosis (OR = 1.80, 95% CI 1.52-2.13) than lower-educated women. Conclusions: Participation in the national breast cancer screening program is strongly associated with improved survival, markedly earlier detection, and substantially reduced mortality risk. Although women with lower education gain the largest absolute survival benefit when they attend screening, their lower participation rates contribute to persistent socioeconomic inequalities. Targeted efforts to increase screening uptake among disadvantaged groups may reduce these disparities. Main messages: Overall, the national breast cancer screening program demonstrates strong effectiveness in improving survival and promoting earlier detection, while highlighting persistent socioeconomic inequalities that require targeted attention.