Breast Cancer Screening (PDQ®)

Mammography is the most widely used screening modality, with solid evidence of benefit for women aged 40 to 74 years. Clinical breast examination and breast self-exam have also been evaluated but are of uncertain benefit. Technologies such as ultrasound, magnetic resonance imaging, tomosynthesis, and molecular breast imaging are being evaluated, usually as adjuncts to mammography.

Benefits

Based on solid evidence, screening mammography may lead to the following benefit:

  • Decrease in breast cancer mortality
    Magnitude of Effect: In the randomized controlled trials (RCTs), for women aged 40 to 74 years, screening with mammography has been associated with a 15% to 20% relative reduction in mortality due to breast cancer.
    [1] Absolute mortality benefit for women screened annually for 10 years is approximately 1% overall, ranging from 4 per 10,000 women who start screening at age 40 years to 50 per 10,000 women who start at age 50 years.[2]
    Study Design: RCTs, population-based evidence.
    Internal Validity: Variable, but meta-analysis of RCTs good.
    Consistency: Fair 
    External Validity: Good.

Harms

Based on solid evidence, screening mammography may lead to the following harms:

  • Overdiagnosis and Resulting Treatment of Insignificant Cancers: Diagnosis of cancers that would otherwise never have caused symptoms or death in a woman’s lifetime can expose a woman to the immediate risks of therapy (surgical deformity or toxicities from radiation therapy, hormone therapy, or chemotherapy), late sequelae (lymphedema), and late effects of therapeutic radiation (new cancers, scarring, or cardiac toxicity).
    Magnitude of Effect: Varies with patient age, tumor type, and grade, and is greater with the first screen than subsequent screening examinations.[3,4] Of all breast cancers detected by screening mammograms, up to 54% are estimated to be results of overdiagnosis.[5
    Study Design: Descriptive population-based comparisons, autopsy series, and series of mammary reduction specimens.
  • False-Positives with Additional Testing and Anxiety.
    Magnitude of Effect: On average, 10% of women will be recalled from each screening examination for further testing, and only 5 of the 100 women recalled will have cancer.[6] Approximately 50% of women screened annually for 10 years in the United States will experience a false-positive, of whom 7% to 17% will have biopsies.[7,8] Additional testing is less likely when prior mammograms are available for comparison. 
    Study Design: Descriptive population-based. 
  • False-Negatives with False Sense of Security and Potential Delay in Cancer Diagnosis.
    Magnitude of Effect: 6% to 46% of women with invasive cancer will have negative mammograms, especially if they are young, have dense breasts,[9,10] or have mucinous, lobular, or rapidly growing cancers.[11
    Study design: Descriptive population-based.
  • Radiation-Induced Breast Cancer: Radiation-induced mutations can cause breast cancer, especially if exposure occurs before age 30 years and is at high doses, such as from mantle radiation therapy for Hodgkin disease. The breast dose associated with a typical two-view mammogram is approximately 4 mSv and extremely unlikely to cause cancer. One Sv is equivalent to 200 mammograms. Latency is at least 8 years, and the increased risk is lifelong.[12,13]
    Magnitude of Effect: Theoretically, annual mammograms in women aged 40 to 80 years may cause up to one breast cancer per 1,000 women.[12,13
    Study design: Descriptive population-based.For all these potential harms of screening mammography, internal validity, consistency and external validity are good.

    Copyright Center of Health™ 4/2014  For permission to reprint this article, please contact the author.