Modern mammography screening and breast cancer mortality: population studyBMJ 2014; 348 doi: https://doi.org/10.1136/bmj.g3701 (Published 17 June 2014) Cite this as: BMJ 2014;348:g3701
- Harald Weedon-Fekjær, researcher123,
- Pål R Romundstad, professor of epidemiology1,
- Lars J Vatten, professor of epidemiology14
- 1Department of Public Health, Norwegian University of Science and Technology, 7491 Trondheim, Norway
- 2Oslo Center for Biostatistics and Epidemiology, Department of Biostatistics, University of Oslo, Oslo, Norway
- 3Oslo Center for Biostatistics and Epidemiology, Research Support Services, Oslo University Hospital, Oslo, Norway
- 4Harvard School of Public Health, Department of Epidemiology, Boston, MA, USA
- Correspondence to: H Weedon-Fekjær
- Accepted 19 May 2014
Objective To evaluate the effectiveness of contemporary mammography screening using individual information about screening history and breast cancer mortality from public screening programmes.
Design Prospective cohort study of Norwegian women who were followed between 1986 and 2009. Within that period (1995-2005), a national mammography screening programme was gradually implemented, with biennial invitations sent to women aged 50-69 years.
Participants All Norwegian women aged 50-79 between 1986 and 2009.
Main outcome measures Multiple Poisson regression analysis was used to estimate breast cancer mortality rate ratios comparing women who were invited to screening (intention to screen) with women who were not invited, with a clear distinction between cases of breast cancer diagnosed before (without potential for screening effect) and after (with potential for screening effect) the first invitation for screening. We took competing causes of death into account by censoring women from further follow-up who died from other causes. Based on the observed mortality reduction combined with the all cause and breast cancer specific mortality in Norway in 2009, we used the CISNET (Cancer Intervention and Surveillance Modeling Network) Stanford simulation model to estimate how many women would need to be invited to biennial mammography screening in the age group 50-69 years to prevent one breast cancer death during their lifetime.
Results During 15 193 034 person years of observation (1986-2009), deaths from breast cancer occurred in 1175 women with a diagnosis after being invited to screening and 8996 women who had not been invited before diagnosis. After adjustment for age, birth cohort, county of residence, and national trends in deaths from breast cancer, the mortality rate ratio associated with being invited to mammography screening was 0.72 (95% confidence interval 0.64 to 0.79). To prevent one death from breast cancer, 368 (95% confidence interval 266 to 508) women would need to be invited to screening.
Conclusion Invitation to modern mammography screening may reduce deaths from breast cancer by about 28%.
To avoid bias by subjective modelling, we developed a detailed analysis protocol and submitted it to the Norwegian Research Council before data delivery from the Norwegian Cancer Registry. This study is based on data from the Cancer Registry of Norway. The interpretation and reporting of these data are the sole responsibility of the authors, and no endorsement by the Cancer Registry of Norway is intended nor should be inferred. We thank Sylvia Plevritis and Diego Munoz for providing inputs needed to derive the number of woman needed to screen to avoid one breast cancer death; these inputs were taken from the Stanford breast cancer screening model, funded by the National Cancer Institute CISNET programme U01CA159256, and were generated for this study.
Contributors: HWF designed the study, collected and analysed the data, and wrote the report. PRR critically reviewed the analyses, interpreted the results, and contributed to the writing of the report. LJV participated in the design, analyses, and interpretation of the results, and wrote the report. HWF and LJV are guarantors of the study.
Funding: This study was supported by the Norwegian Research Council (reference No 189503).
Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.
Ethical approval: This study was approved by the regional committee for ethics in medical research.
Data sharing: The data are available for research projects from the legal administrator of the data, the Norwegian Cancer Registry. For data requests use <email@example.com>/.
Transparency: The lead author (the manuscript’s guarantor) affirms that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.
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