Screening mammography - Harvard Health Publishing

Screening mammography

Published: September, 2005

The release of updated breast cancer screening guidelines from the United States Preventive Services Task Force (USPSTF) in November 2009 sparked a heated national debate about how best to use screening mammography. The USPSTF asked an expert panel to re-examine the scientific evidence on the effectiveness of breast cancer screening in women ages 40 and older who are at average risk for developing breast cancer.

The USPSTF concluded that the use of mammography, clinical breast exam, and breast self-exam should be scaled back. The most controversial recommendations were to delay routine screening mammography until age 50 (previous guidelines recommended mammography screening every one to two years for women in their 40s) and to screen women in their 50s and 60s only once every two years, rather than annually, as the earlier guidelines had advised.

Many physicians, researchers, health organizations, advocacy groups, politicians, and individual women reacted with concern to the guidelines. That's because breast cancer is the second leading cause of cancer death among women in the United States.

Mammography screening has been the foundation of breast cancer prevention in this country since the 1980s. Since 1990, breast cancer mortality has been decreasing at a fairly steady 2% per year, and many experts attribute that decrease to a combination of regular screening mammography and improved treatment.

Summary of the USPSTF recommendations on screening for breast cancer

  • The USPSTF recommends against routine screening mammography in women in their 40s who aren't at increased risk for breast cancer. The decision to start mammography before age 50 should be based on a woman's risk for breast cancer and personal preferences about the benefits and harms.
  • The USPSTF recommends mammography every two years for women ages 50 to 74.
  • Current evidence is not sufficient to assess the effectiveness of screening mammography in women ages 75 and over.
  • Current evidence is not sufficient to assess the effectiveness of clinical breast exam in addition to screening mammography.
  • The USPSTF recommends against clinicians teaching women breast self-examination.
  • Current evidence is not sufficient to assess the additional effectiveness of digital mammography or breast MRI instead of film mammography for breast cancer screening.

Source: Annals of Internal Medicine, Nov. 17, 2009, pp. 716–726. The recommendations may also be viewed online, at

Why review an effective screening program?

The panel reviewed all clinical trials of screening mammography with more than 10 years of follow-up. They found that starting at age 40, screening mammography reduces breast cancer mortality overall by 15% — about the same as in 2002. But this time, the panel also tried to determine how the benefits of screening (lives saved) stacked up against the harms. Many mammograms that are initially interpreted as "positive"—as indicating a possible cancer—turn out to be "falsely positive": the spot that looks like cancer on the x-ray turns out not to be cancer. But that fact is only discovered after more testing and biopsies that, in retrospect, were unnecessary, and only after several weeks of terrible worry.

The panel concluded that screening women starting at age 40 would reduce breast cancer deaths by only a modest amount, compared with screening starting at a later age—in large part because breast cancer is less common in women age 40-49 than in women age 50 or older. Women in their 40s also have more false positive mammograms, because their breasts are denser, making cancers harder to spot. To avoid one breast cancer death, 1,904 women in their 40s would need to be screened, and many of those women would have false positive results that led to more testing, biopsies, and worry.

In women in their 50s, one life would be saved for every 1,339 women screened, and for those in their 60s, screening just 377 women would yield one life saved. According to the USPSTF's model, screening women in their 40s for breast cancer does not make good public health sense because there is no net benefit: the number of deaths prevented is too small, and the potential harm from false positive test results is too great.

Debate not over

Breast cancer and imaging experts have weighed in for and against the revised guidelines. Advocates welcome what they regard as a serious consideration of the risks, compared with the benefits, welcoming the potential reduction in unnecessary biopsies and psychological stress. Opponents point to a falling breast cancer death rate that's due, in part, to annual screening mammography. Some reject the statistical models used by the USPSTF. The debate will surely continue.

What now?

For now:

  • Talk to your clinician about the implications of the recommendations for you. Physicians are not obliged to discontinue or cut back on screening.
  • The revised guidelines apply to women at average risk of developing breast cancer. Know your own risks and work with your clinician to develop a screening strategy that's right for you.
  • If you're in your 40s, you're not prohibited from having screening mammography. The USPSTF recommends that you make an informed decision based on your personal preferences and medical history.

If you're in your 70s, have a frank discussion with your clinician about the benefits and harms of breast cancer screening.

March 2010 update

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