The Bottom Line - SGIM

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Apr 8, 2014 - Not Screened with Mammography. 0. 1000. 2000. 3000. 4000. 5000. 6000. 7000. 8000 ... Gøtzsche PC, Jørgen
The Bottom Line

April 8, 2014

Long Term Follow-up of Screening Mammography

25 year follow-up for breast cancer incidence & mortality of the Canadian National Breast Screening Study: Randomised screening trial1 STRENGTH OF EVIDENCE: MODERATE

Why is this important? The benefits and harms of screening mammography remain controversial. Systematic reviews have shown a small benefit of screening mammography, as well as certain harms2. This is a twenty-five year follow-up of a large randomized trial of mammography.

Facts §§ The Canadian National Breast Screening Study randomized 89,835 women to receive either annual mammography plus breast examination or breast examination alone. The breast examination was an initial breast exam followed by usual community care for participants ages 40 to 49 or an annual breast examination for those ages 50-59. The intervention lasted for 5 years. The current study presented long-term follow-up over an average of 22 years. All breast exams were performed by trained nurses and took approximately 10 minutes3. Over the course of 22 years:

Outcomes Among Women Screened with Mammography 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0

overdiagnoses

deaths from breast cancer

612 nonfatal breast cancer

10000 9000 8000

§§ The study estimated that 23 in 10,000 women in the mammography group were diagnosed and treated for breast cancer which never would have made them sick, known as “overdiagnosed” cancer.

2000 1000

Bottom Line

108

Outcomes Among Women Not Screened with Mammography

§§ 108 in 10,000 women died of breast cancer in the mammography group and 110 in 10,000 women died of breast cancer in the control group. Mammography had no effect on breast cancer mortality.

The

23

7000 6000 5000 4000 3000

0

0*

110

overdiagnoses

deaths from breast cancer

585 nonfatal breast cancer

*overdiagnoses in control group set at zero as baseline for comparison with screened group

Mammography screening, compared with clinical breast exam, over a 5 year period did not prevent mortality after 22 years of follow up in a large Canadian study. Overdiagnosis of a clinically insignificant cancer was seen in 23 in every 10,000 screened women.

Strength of Evidence (Adapted from Guyatt G BMJ, 26 April 2008) This refers to the degree to which the findings of this study are likely to be free of bias. High Moderate Low Very low

Tips for Discussion of Results with Patients §§ In this study, annual mammography plus clinical breast exam did not prevent mortality compared with a thorough clinical breast exam alone after long-term follow-up. §§ Annual mammography detected a significant number of small, non-palpable breast cancers, but approximately half of these were examples of overdiagnosis. Overdiagnosis of a clinically insignificant breast cancer occurred in approximately 23 of 10,000 women screened. §§ This data is already reflected in meta-analyses which have estimated that mammography does prevent breast cancer mortality2, so it may not change our overall understanding of the benefits of mammography.

References 1.

Miller AB et al. BMJ 2014; 348:G366

2.

Gøtzsche PC, Jørgensen KJ. Screening for breast cancer with mammography. Cochrane Database Syst Rev. 2013;(6):CD001877.

3.

Miller AB et al. JNCI 2000 92(18):1490-9

Written by the Evidence-Based Medicine Task Force Deborah Korenstein, MD

Zackary Berger, MD, PhD

Scott Kaatz, DO, MSc

Jeremy Sussman, MD, MSc

Rebecca Beyth, MD, MSc

M.E. Beth Smith, DO

KoKo Aung, MD, MPH

Daniel Elliott, MD, MSCE

Daniella Zipkin, MD

The Bottom Line summaries reflect the expertise and opinions of the SGIM EBM Task Force as of the date of release of this summary.

April 8, 2014

The Bottom

Line

25 year follow-up for breast cancer incidence & mortality of the Canadian National Breast Screening Study: Randomised screening trial1

2