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Evidence Summary

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Breast cancer deaths are decreased by mammography screening even in women at average risk

Myers ER, Moorman P, Gierisch JM, et al. Benefits and Harms of Breast Cancer Screening: A Systematic Review. JAMA. 2015;314:1615-34.

Review questions

In women 40 years of age or older who have no risk factors for breast cancer, does mammography screening reduce breast cancer deaths? Are there false-positive results? In women 20 years of age or older who have no risk factors for breast cancer, does clinical breast examination reduce breast cancer deaths? Are there false-positive results?

Background

Breast cancer screening involves regular examination of women’s breasts to detect cancer. There are different ways to screen for breast cancer including mammography (x-rays of the breast) and clinical breast exam.

Early detection of breast cancer by screening is more likely to detect the cancer when it is small and has had less chance to spread. This allows more treatment options and often a better outcome. However, breast cancer screening may also produce false-positive results and lead to unnecessary tests (such as biopsies) and stress.

How the review was done

The researchers did a systematic review based on studies available up to March 2014.

They found 82 studies, including systematic reviews, randomized controlled trials, and observational studies.

Key features of the studies were:

  • women in mammography studies were 40 years of age or older;
  • women in clinical breast exam studies were 20 years of age or older; and
  • women did not have any risk factors for breast cancer.

What the researchers found

Mammography

The effects of mammography on breast cancer deaths and the risk of false-positive results that lead to biopsies are in the Table.

Clinical breast exam

No clinical trials reported the effect of clinical breast exams on breast cancer deaths.

1% to 6% of women who had clinical breast exams had false-positive results.

Conclusion

Breast cancer deaths are decreased by mammography screening, even in women at average risk, but mammography can produce false-positive results leading to additional testing. The effect of clinical breast examination on breast cancer deaths is unknown, but it does produce false-positive results.

Mammography screening in women 40 years of age and older with no risk factors for breast cancer–key results

Breast cancer deaths after 13 years

False-positive results leading to biopsies

In all women 40 years of age and older, mammography reduced breast cancer deaths compared with no mammography

In women having their first mammographies, 2% of women 40 to 44 years of age and 3% of women 55 to 59 years of age had false-positive results that led to biopsies

In women having second or later mammographies, 0.8% of women 40 to 44 years of age and 1.5% of women 55 to 59 years of age had false-positive results that led to biopsies

In women 40 to 49 years of age, mammography reduced breast cancer deaths compared with no mammography

Compared with women 40 to 44 years of age, women 45 to 49 years of age who had mammographies were more likely to have false-positive results that led to biopsies

In women 50 years of age and older, mammography reduced breast cancer deaths compared with no mammography

Compared with women 40 to 44 years of age, women 50 to 54 and 55 to 59 years of age who had mammographies were more likely to have false-positive results that led to biopsies

In women 60 to 69 years of age, mammography reduced breast cancer deaths compared with no mammography

Compared with women 40 to 44 years of age, women 60 to 64 years of age who had mammographies were not more likely to have false-positive results that led to biopsies

Compared with women 40 to 44 years of age, women 65 years of age and older who had mammographies were more likely to have false-positive results that led to biopsies

In women 70 to 74 years of age, mammography did not reduce breast cancer deaths compared with no mammography

Compared with women 40 to 44 years of age, women 65 years of age and older who had mammographies were more likely to have false-positive results that led to biopsies

Mammographies more frequently than every 24 months reduced risk of breast cancer death in women 40 to 44 and 50 to 69 years of age

For women who have their first mammographies at 40 years of age, about 7% of women screened had false-positive results that led to biopsies within 10 years

For women who have their first mammographies at 50 years of age, about 9% of women screened annually had false-positive results that led to biopsies within 10 years

Mammographies every 24 months or less frequently reduced breast cancer deaths in women 50 to 69 years of age but not in women 40 to 49 years of age

For women who have their first mammographies at 40 years of age, about 5% of women screened every other year had false-positive results that led to biopsies within 10 years

For women who have their first mammographies at 50 years of age, about 6% of women screened every other year had false-positive results that led to biopsies within 10 years

 




Glossary

Clinical trials
Studies where people are assigned to one of the treatments but not purely by chance.
False-positive
A test result that suggests the presence of a disease which turns out not to be there.
Observational studies
Studies where the treatment that each person receives is beyond the control of the researcher.
Randomized controlled trials
Studies where people are assigned to one of the treatments purely by chance.
Risk factors
Aspects making a condition more likely.
Systematic review
A comprehensive evaluation of the available research evidence on a particular topic.

Related Evidence Summaries

Related Web Resources

  • Breast cancer: Risks and benefits, age 50-69

    Canadian Task Force on Preventive Health Care
    Your risk of dying from breast cancer is slightly reduced if you have regular screening. However, regular screening increases your chance of a false positive result, a biopsy and having part or all of a breast removed unnecessarily.
  • Breast cancer: Patient algorithm

    Canadian Task Force on Preventive Health Care
    The Canadian Task Force on Preventive Health Care recommends women between 50 and 74 years old who are not at high risk get screened for breast cancer every 2 to 3 years. Talk to your doctor about screening options if you are at high risk or over 74 years old.
  • Breast cancer: Patient FAQ

    Canadian Task Force on Preventive Health Care
    This resource includes frequently asked questions about breast cancer, including: Who is considered high risk? What are the harms associated with mammography? and Why is routine screening NOT recommended for women 40-49 years?
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