Breast cancer mortality after implementation of organized population-based breast cancer screening in Norway
Menée en Norvège à partir des données de registres nationaux portant sur 1 340 333 femmes, cette étude évalue l'effet d'un programme biennal de dépistage du cancer du sein, destiné aux femmes de 50 à 69 ans et comportant une mammographie, sur la mortalité spécifique
Background : We estimated breast cancer (BC) mortality reduction associated with invitations to a nation-wide population based screening program and changes in treatment, in Norway.
Material and methods : Breast Screen Norway started in 1996 and became nationwide in 2005. It invites women aged 50–69 to biennial mammographic screening. We retrieved individual-level data for 1,340,333 women from national registries. During 1996–2014 (screening window), women contributed person-years (PY) in non-invited and invited periods. We created comparable periods for 1977–1995 (pre-screening window) by dividing the follow-up time for each woman into a pseudo-non-invited and pseudo-invited periods. We estimated BC mortality for the four periods, using the so-called evaluation model: counting BC deaths in each period for all women diagnosed within the period, counting BC deaths and person-years after screening-age only for women diagnosed within screening-age. We used a multivariable flexible parametric survival model to estimate hazard ratio (HR) for the effect of invitation and improved treatment.
Results : There were 5818 BC deaths across 16,533,281 PY. Invitations to screening reduced BC mortality by 20% (HR: 0.80, 95%CI: 0.70-0.91) among women ≥50 years old and by 25% (HR: 0.75, 95%CI: 0.65-0.86) among screening-aged women. The treatment effect was 23% (HR: 0.77, 95%CI: 0.65-0.92) for women ≥50 years old, and 17% (HR: 0.83, 95%CI: 0.74-0.94) for screening-aged women.
Conclusion : We observed a similar reduction in BC mortality associated with invitations to screening and improvements in treatment among women ≥50 years old, during 1977–2014.
Journal of the National Cancer Institute , résumé, 2018