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FACTS FOR BREAST CANCER SCREENING

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Findings of a systematic review of the benefits and harms of breast cancer screening commissioned by the American Cancer Society (ACS) to inform its updated guideline on screening in average-risk women were reported in JAMAby Myers et al of the Duke Evidence Synthesis Group. Their findings were published along with the updated ACS guideline.
The review included literature searches through March 2014, yielding 7 reviews, 10 randomized clinical trials, 72 observational studies, and 1 modeling study providing relevant data. Key findings of the systematic review are reproduced here.
Key Findings
  • Across all ages of women at average risk, pooled estimates of the association between mammography screening and mortality reduction after 13 years of follow-up were similar for 3 meta-analyses of clinical trials: relative risk (RR) = 0.80, 95% confidence interval [CI] = 0.73–0.89, in a UK Independent Panel analysis; RR = 0.82, 95% CI = 0.74–0.94, in a Canadian Task Force analysis; and RR = 0.81, 95% CI = 0.74–0.87, in a Cochrane analysis.
  • Risk reduction was greater in a meta-analysis of cohort studies (RR = 0.75, 95% CI = 0.69–0.81) and similar in a modeling study (Cancer Intervention and Surveillance Modeling Network; median RR equivalent among seven models = 0.85 (range = 0.77–0.93).
  • There is uncertainty about the magnitude of screening-associated mortality reduction in the entire U.S. population, among women aged 40 to 49 years, and with annual vs biennial screening.
  • There is uncertainty about the magnitude of overdiagnosis associated with different screening strategies, attributable in part to a lack of consensus on methods of estimation and the importance of ductal carcinoma in situ in overdiagnosis.
  • For women with a first mammography screening at age 40 years, the estimated 10-year cumulative risk of a false-positive biopsy result was higher with annual (7.0%, 95% CI = 6.1%–7.8%) than biennial screening (4.8%, 95% CI = 4.4%–5.2%). Ten-year probabilities of false-positive biopsy results were similar among women first screened at age 50 years, but indirect estimates of lifetime probability of false-positive results were lower.
  • Evidence for the relationship between screening and life expectancy and quality-adjusted life expectancy was of low quality.
  • There was no direct evidence for any additional mortality benefit associated with the addition of clinical breast examination to mammography. Observational evidence from the United States and Canada suggested an increase in false-positive findings compared with mammography alone, with both studies finding an estimated 55 additional false-positive findings per extra breast cancer detected with the addition of clinical breast exam.
The investigators concluded: “For women of all ages at average risk, screening was associated with a reduction in breast cancer mortality of approximately 20%, although there was uncertainty about quantitative estimates of outcomes for different breast cancer screening strategies in the United States. These findings and the related uncertainty should be considered when making recommendations based on judgments about the balance of benefits and harms of breast cancer screening.”
The study was funded by the American Cancer Society.

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