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False-Positive Results Common with Annual Screening Mammography

Among women who start annual screening mammography at the age of 40, more than half will have a false-positive result (the need to return for additional imaging even though no cancer is present) during the first 10 years of screening. Seven percent of cancer-free women will be advised to have a breast biopsy. These results were published in the Annals of Internal Medicine. 

A mammogram is an X-ray of the breast. A screening mammogram is a mammogram that is performed in a woman without breast symptoms. The goal of screening mammography is to detect breast cancer at an early stage when it is most easily treated.    

Different groups of experts have reached different conclusions about when mammographic screening should begin and how often it should be performed. The U.S. Preventive Services Task Force recommends that routine screening of average-risk women begin at age 50 and be performed every two years. The American Cancer Society recommends annual screening beginning at age 40. Women may wish to talk with their doctor about the approach that’s right for them.    

Although screening mammography reduces the risk of death from breast cancer, there are risks to any screening program. One of these risks is a false-positive test result; this is a result that suggests that cancer may be present even though the person is actually cancer-free. False-positive results can lead to anxiety and unnecessary additional testing.    

To explore how the frequency of false-positive results varies with different approaches to screening, researchers conducted a study among almost 170,000 women who had a first screening mammogram at age 40 to 59 years, and 4,400 women with breast cancer.

The researchers evaluated false-positive recalls (asking a cancer-free woman to return for additional imaging) as well as false-positive biopsy recommendations (recommending that a cancer-free woman have a breast biopsy).   

  • Among women who started screening at the age of 40, the likelihood of having a false-positive recall during 10 years of screening was 61% for women who were screened every year and 42% for women who were screened every two years. The likelihood of a false-positive biopsy recommendation was 7% for women screened every year and 5% for women screened every two years. 
  • Estimates were similar when women started screening at the age of 50, but the lifetime risk of a false-positive result was lower because they had a decade less of screening. 
  • A false-positive recall was less likely for women who had a previous mammogram available for comparison. 
  • Among women diagnosed with breast cancer, those who had been screened every two years were somewhat more likely than women screened every year to be diagnosed with late-stage cancer. This result was not statistically significant, however, suggesting that it could have occurred by chance alone. 

These results suggest that performing screening mammography every two years (rather than every year) will reduce the frequency of false-positive test results, but may also be linked with a small increase in the risk of being diagnosed with later-stage breast cancer.     

In another study published in the same issue of the Annals of Internal Medicine, researchers compared how well two different types of mammograms—film and digital—detected breast cancer. The two approaches performed similarly in most women, although digital mammography appeared to be better than film mammography at detecting estrogen receptor-negative breast cancers and breast cancers in women with very dense breasts. Because these cancers are more common in younger women, younger women may wish to choose digital mammography if they are screened.  Women are advised to talk with their healthcare provider about the approach to breast cancer screening that’s right for them. 

References:  

Posted October 27, 2011

[1] Hubbard RA, Kerlikowske K, Flowers CI et al. Cumulative probability of false-positive recall or biopsy recommendations after 10 years of screening mammography. A cohort study. Annals of Internal Medicine. 2011;155:481-492. 

[2] Kerlikowske K, Hubbard RA, Miglioretti DL et al. Comparative effectiveness of digital versus film-screen mammography in community practice in the United States. A cohort study. Annals of Internal Medicine. 2011;155:493-502.