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

• Published in: International journal of cancer 2019-02, Vol.144 (4), p.697-706
• Main Authors: Møller, Mette H., Lousdal, Mette Lise, Kristiansen, Ivar S., Støvring, Henrik
• Format: Article
• Language: English
• Subjects: Adult; Age; Aged; Aged, 80 and over; Breast cancer; Breast Neoplasms - diagnosis; Breast Neoplasms - epidemiology; Breast Neoplasms - mortality; Cancer; Cohort analysis; Cohort Studies; Early Detection of Cancer - methods; Female; Health risk assessment; Humans; Incidence; Mammography; Mammography - methods; mass screening; Mass Screening - methods; Medical research; Middle Aged; Mortality; Norway - epidemiology; Population studies; Population-based studies; Survival Rate
• ISSN: 0020-7136; 1097-0215
• DOI: 10.1002/ijc.31832

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. What's new? Recent improvements in breast cancer awareness and treatment have raised questions about whether mammography screening programs are effective in reducing breast cancer mortality. Here, estimation of relative incidence‐based mortality rate ratios among women in birth cohorts 1896–1982 in the Cancer Registry of Norway shows no difference in breast cancer mortality changes between women who were eligible for mammography screening compared with women outside the screening age range. Women who were too young or too old for screening and women who were eligible for screening experienced similar mortality reductions. The results were comparable for subsequent analyses using different methodologies.