A Cochrane review [Abstract] 1 included 8 randomised trials comparing mammographic screening with no mammographic screening. One biased trial was excluded and 600 000 women aged 39 to 74 years were included in the analyses.
Abstract and full text in Cochrane database (licence for full text required) http://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD001877.pub5/full
A detailed discussion on breast cancer screening is available in IARC handbook of cancer prevention published by WHO 2http://publications.iarc.fr/Book-And-Report-Series/Iarc-Handbooks-Of-Cancer-Prevention/Breast-Cancer-Screening-2016. Women aged 50-69 years invited to service mammography screening had, on average, a 24% reduced risk of mortality from breast cancer, and women who attended service mammography screening had, on average, about a 40% reduced risk of mortality from breast cancer. Screening women aged 70-74 years by mammography also reduced breast cancer mortality. There was limited evidence that screening women aged 40-49 years was associated with a reduction of about 20% in risk of breast cancer mortality. The percentage of overdiagnosis ranged from 1% to 10% when estimated by comparing thecumulative incidence of breast cancer in womenscreened from age 50-69 years and followed upfor about 10 years after the last screen with thecumulative incidence of breast cancer in similarbut unscreened women over the same period oftime.
The European Commission Initiative on Breast Cancer (ECIBC) guidelines show detailed evidence on breast cancer screening at different ages 3http://healthcare-quality.jrc.ec.europa.eu/european-breast-cancer-guidelines.
A Swedish prospective registry based study 4 estimated the effect of participation in successive mammographic screening examinations on breast cancer mortality. Women were diveded to groups according to whether they had participated in the most recent screening examination prior to diagnosis only (intermittent participants, n=41 746), the penultimate screening examination only (lapsed participants, n=30 945), both examinations (serial participants, n=392 135), or neither examination (serial nonparticipants, n=84 265). Serial participants had a 49% lower risk of breast cancer mortality (RR 0.51; 95% CI 0.48 to 0.55) and a 50% lower risk of death from breast cancer within 10 years of diagnosis (RR 0.50; 95% CI 0.46 to 0.55) than serial nonparticipants. Lapsed and intermittent participants had a smaller reduction. Serial participants had significantly lower risk of both outcomes than lapsed or intermittent participants.
A systematic review 5 included 10 RCTs with a total of 616 641 women aged 38-75. Mammography reduced breast cancer mortality in women aged 50-69 (RR 0.77, 95% CI 0.66 to 0.90). In women aged 70-74 years and under 50s, mortality was reduced statistically non-significantly (RR 0.77, 95% CI 0.54 to1.09 and RR 0.88, 95% CI 0.76 to 1.02, respectively). Mammography reduced stage IIA+ in women aged 50-69 (RR 0.80, 95% CI 0.64 to 1.00) but resulted in an overdiagnosis probability of 17% (95% CI 15 to 20%).
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