Background: Medical organizations generally agree on the benefits of mammography to screen for breast cancer in asymptomatic women 50 years and older. However, routine screening in younger women remains controversial because of the closer balance of risks and benefits. Although breast cancer is a common cause of death for women in their 40s, it affects less than 2 percent of women in this age group. Most women who do not have cancer will nonetheless be exposed to the potential harms of mammography, which include pain, radiation exposure, and psychological and physical consequences of false-positive results (e.g., needle biopsy). Armstrong and colleagues systematically reviewed the risks and benefits of screening mammography for women in their 40s to form a clinical practice guideline from the American College of Physicians.

The Study: Data sources for this systematic review included English-language articles identified in multiple electronic databases and article reference lists through May 2005. The authors searched for literature on the effect of screening mammography on breast cancer mortality rates and breast cancer treatment; and the risks of screening mammography, including radiation, overdiagnosis, and false-positive results. Initial searches retrieved 873 full-text articles. These articles were reviewed for relevance and quality by two study investigators; 117 articles met inclusion criteria.

Results: A recent meta-analysis of randomized trials found a 15 percent decrease in breast cancer mortality for women in their 40s after 14 years of follow-up (relative risk = 0.85; 95% confidence interval, 0.73 to 0.99). Previous meta-analyses have found 7 to 23 percent decreases in breast cancer mortality; variations result from differences in quality assessment and study inclusion. Because screening mammography detects localized cancers more effectively than does clinical diagnosis, women whose cancers are found by screening are more likely to undergo breast surgery and less likely to require chemotherapy or hormone therapy.

Indirect evidence from studies of other radiation sources suggests that the risk of developing breast cancer from low-dose radiation exposure during mammography is extremely small. No studies have evaluated the risk of overdiagnosis (i.e., detection of breast cancer that would not have produced symptoms during a person's lifetime) from mammography in women in their 40s. Although studies have documented high rates of false-positive results (20 to 56 percent after 10 mammograms), women with false-positive results were not discouraged from having future screenings and did not suffer permanent psychological effects. Pain and discomfort from mammography varied but did not prevent most women from having future screenings.

Conclusion: The authors conclude that although women in their 40s who undergo screening mammography have a lower risk of breast cancer–related death, screening also results in harms that may be clinically significant for some women. The authors suggest that an individualized risk assessment, taking into account patient factors such as family history and the value attached to a false-positive test result, may be appropriate to guide decisions about breast cancer screening in this age group.

editor's note: Echoing the conclusions of the systematic review by Armstrong and colleagues, an accompanying American College of Physicians clinical practice guideline recommends individualized risk assessment and shared decision making for women in their 40s who are considering breast cancer screening.¹ This guideline differs from recommendations of other organizations. For example, the U.S. Preventive Services Task Force (USPSTF) recommends screening mammography every one to two years for women 40 years and older.² The USPSTF is currently updating its recommendation.—k.l.