Am Fam Physician. 2005 Nov 1;72(9):1860.
Mammography and other types of breast cancer screening have been recommended for many years. In most mammography studies, women are observed in the highly controlled setting of randomized trials. Elmore and colleagues conducted a systematic review of breast cancer mortality and new screening modality test characteristics. The aim was to provide information about the effectiveness of mammography, based on community practice, and to look at the role of new imaging techniques in screening for breast cancer. The authors conducted a search of the Cochrane Library, MEDLINE, and other resources to find English-language studies about breast cancer screening.
Recent concerns about study flaws, which led to questioning of mammography’s effectiveness, have not been confirmed. This is especially true among women 50 to 69 years of age, in whom meta-analysis shows a reduction in breast cancer mortality of 20 to 35 percent with mammography. In women in their 40s, the benefit is less clear. An estimated 500 to 1,800 40-year-old women would need to be screened on a regular basis to prevent one breast cancer death in 14 to 20 years. Few studies have included women older than 70 years; however, it is reasonable to continue screening older women who have a life expectancy greater than five years.
Overall sensitivity of mammography is 75 percent, and specificity is 92.3 percent; sensitivity increases with age. The recall rate is twice as high in the United States as in the United Kingdom, with no difference in cancer detection rate. This could be caused by many factors, including the United Kingdom’s more stringent requirements for minimum number of yearly mammography interpretations, or because of increased malpractice concerns in the United States.
Newer screening modalities include full-field digital mammography, computer-aided detection programs, magnetic resonance imaging (MRI), and ultrasonography. Digital mammography provides convenience but has not proved to be as successful at detecting cancer as screen-film mammography; it also costs more and may result in higher recall rates. Computer-aided detection programs show mixed results, with the largest study showing no differences in detection and recall rates. High-risk women may benefit from the apparent increased sensitivity of MRI; however, MRI may have decreased specificity and is much more expensive than mammography. Ultrasonography has not been well studied in the general population. The review found that false-positive rates ranged from 2.4 to 12.9 percent. In high-risk women, ultrasonography may detect three to four additional cancers per 1,000 women.
Clinical breast examinations probably are not highly accurate in the community setting, with 40 percent of physicians in one study using no methodical approach to the search for breast masses. Breast cancer diagnosis is increased by a likelihood ratio of 2.1 when a breast abnormality is found in a community practice, substantially lower than the likelihood ratio with mammography. Breast self-examination has not improved mortality outcomes but has increased false-positive rates.
The authors note that in addition to discomfort and false-positive rates related to mammography, radiation exposure may pose an additional risk to the breast. However, the benefit-to-harm ratio increases with age.
Elmore JG, et al. Screening for breast cancer. JAMA. March 9, 2005;293:1245–56.
Copyright © 2005 by the American Academy of Family Physicians.
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