Swedish Two-County Trial: Impact of Mammographic Screening on Breast Cancer Mortality during 3 Decades
- László Tabár, MD,
- Bedrich Vitak, MD,
- Tony Hsiu-Hsi Chen, PhD,
- Amy Ming-Fang Yen, PhD,
- Anders Cohen, MD,
- Tibor Tot, MD,
- Sherry Yueh-Hsia Chiu, PhD,
- Sam Li-Sheng Chen, PhD,
- Jean Ching-Yuan Fann, PhD,
- Johan Rosell, PhD,
- Helena Fohlin, MSc,
- Robert A. Smith, PhD and
- Stephen W. Duffy, MSc
- From the Departments of Mammography (L.T.), Surgery (A.C.), and Pathology (T.T.), Falun Central Hospital, Falun, Sweden; Department of Mammography, University of Linköping, Linköping, Sweden (B.V.); Graduate Institute of Epidemiology and Preventive Medicine, National Taiwan University, Taipei, Taiwan (T.H.H.C.); School of Oral Hygiene, Taipei Medical University, Taipei, Taiwan (A.M.F.Y., S.L.S.C.); Department and Graduate Institute of Health Care Management, Chang Gung University, Taoyuan, Taiwan (S.Y.H.C.); Department of Nutrition and Health Sciences, Kainan University, Taoyuan, Taiwan (J.C.Y.F.); Regional Cancer Center, Southeast Sweden, University Hospital, Linköping, Sweden (J.R., H.F.); American Cancer Society, Atlanta, Ga (R.A.S.); and Cancer Research UK Centre for Epidemiology, Mathematics and Statistics, Wolfson Institute of Preventive Medicine, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, Charterhouse Square, London EC1M 6BQ, England (S.W.D.).
- Address correspondence to
S.W.D. (e-mail: s.w.duffy{at}qmul.ac.uk).
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Author contributions: Guarantor of integrity of entire study, L.T.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, L.T., S.Y.H.C., R.A.S., S.W.D.; clinical studies, L.T., B.V., A.C., T.T., H.F.; statistical analysis, T.H.H.C., A.M.F.Y., S.Y.H.C., S.L.S.C., J.C.Y.F., J.R., H.F., S.W.D.; and manuscript editing, L.T., B.V., T.H.H.C., A.M.F.Y., R.A.S., S.W.D.
Abstract
Purpose: To estimate the long-term (29-year) effect of mammographic screening on breast cancer mortality in terms of both relative and absolute effects.
Materials and Methods: This study was carried out under the auspices of the Swedish National Board of Health and Welfare. The board determined that, because randomization was at a community level and was to invitation to screening, informed verbal consent could be given by the participants when they attended the screening examination. A total of 133 065 women aged 40–74 years residing in two Swedish counties were randomized into a group invited to mammographic screening and a control group receiving usual care. Case status and cause of death were determined by the local trial end point committees and, independently, by an external committee. Mortality analysis was performed by using negative binomial regression.
Results: There was a highly significant reduction in breast cancer mortality in women invited to screening according to both local end point committee data (relative risk [RR] = 0.69; 95% confidence interval: 0.56, 0.84; P < .0001) and consensus data (RR = 0.73; 95% confidence interval: 0.59, 0.89; P = .002). At 29 years of follow-up, the number of women needed to undergo screening for 7 years to prevent one breast cancer death was 414 according to local data and 519 according to consensus data. Most prevented breast cancer deaths would have occurred (in the absence of screening) after the first 10 years of follow-up.
Conclusion: Invitation to mammographic screening results in a highly significant decrease in breast cancer–specific mortality. Evaluation of the full impact of screening, in particular estimates of absolute benefit and number needed to screen, requires follow-up times exceeding 20 years because the observed number of breast cancer deaths prevented increases with increasing time of follow-up.
© RSNA, 2011
Footnotes
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Received March 22, 2011; revision requested April 14; revision received May 2; accepted May 3; final version accepted May 5.
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Supported by the County Councils of Kopparberg (now Dalarna) and Östergötland and the American Cancer Society through a gift from the Longaberger Company’s Horizon of Hope Campaign.
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- Abbreviations:
- ASP =
- active study population
- PSP =
- passive study population
- RR =
- relative risk
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