Demography

Cohort

Cohort study

Mammography

Environmental health

Breast cancer screening

Physics

Optics

Relative risk

Population

Internal medicine

Sociology

Obstetrics

Confidence interval

Gynecology

Medicine

Breast cancer

Incidence (geometry)

Cancer

International Journal of Cancer

We aimed to estimate the effect of organized mammography screening on incidence-based breast cancer mortality by comparing changes in mortality among women eligible for screening to concurrent changes in younger and older ineligible women. In a county-wise balanced, open-cohort study, we used birth cohorts (1896-1982) to construct three age groups in both the historical and screening period: women eligible for screening, and younger or older women ineligible for screening. We included women diagnosed with breast cancer who died within the same age-period group during 1987-2010 (n = 4,903). We estimated relative incidence-based mortality rate ratios (relative MRR) comparing temporal changes in eligible women to concurrent changes in ineligible women. Additionally, we conducted analyses comparing the change in eligible women to younger, ineligible women with either continued accrual and follow-up period (eligible women only) or continued follow-up period. All three age groups experienced a reduction in mortality, but the decrease among eligible women was about the same among ineligible women (relative MRR = 1.05, 95% CI: (0.94-1.18)). Varying the definition of follow-up yielded similar results. Mammography screening was not associated with a larger breast cancer mortality reduction in women eligible relative to ineligible women.

Effect of organized mammography screening on breast cancer mortality: A population-based cohort study in Norway