Women with dense breasts or a first-degree relative with breast cancer are twice as likely as average-risk women to develop breast cancer in their 40s and these women would benefit from beginning mammography screening at age 40, according to the results of two studies published in the Annals of Internal Medicine.
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 (USPSTF) recommends that routine screening of average-risk women begin at age 50 and be performed every two years. In contrast, the American Cancer Society (ACS) recommends annual screening beginning at age 40.
The 2009 USPSTF screening recommendation to delay screening until age 50 created enormous controversy. Sometimes, screening average-risk women in their 40s can cause more harm than benefit and can result in false-positive test results and overdiagnosis. However, some women do benefit from earlier screening. These new studies were designed to identify women who might benefit from beginning screening at age 40—and they represent a shift away from the one-size-fits-all approach and toward personalized screening recommendations.
In the first study, researchers conducted a comprehensive review of 66 studies in addition to analyzing new data from over 380,000 women in order to evaluate breast cancer risk for women in their 40s. They found that women who have a mother or sister with breast cancer have double the risk of developing the disease. What’s more—those with more than one first-degree relative with breast cancer have nearly four times the risk of developing the disease.
The study also found that women with dense breasts—meaning the breasts have substantially more glandular tissue than fat—are twice as likely to develop breast cancer in their 40s. The researchers identified other risk factors as well: women who have had breast biopsies that turned out to be benign have an 80% greater risk of getting the disease in their 40s; women on oral contraceptives have a 30% increased risk; women who have never given birth have a 25% greater risk; and women who had their first child after age 30 have a 20% increased risk.
The second study was designed to identify the threshold of risk necessary in order for the benefits to outweigh the harms in screening women in their 40s. The researchers analyzed data from screening average-risk women aged 50 to 74 in order to determine the rate of false-positives and deaths averted by screening. Next they used four independent simulation models for women ages 40 to 49. They found that the benefits and harms from screening mammograms every two years for women 40-49 with a twofold increase in breast cancer risk are similar to those for average-risk women who begin biennial screening at age 50. Women with a fourfold increased risk benefited from yearly screening starting at age 40.
The bottom line—one size does not fit all when it comes to breast cancer screening. By determining a woman’s risk of developing the disease, doctors can create personalized screening recommendations and ensure the benefits of screening outweigh the harms.
 Nelson HD, Zakher B, Cantor A, et al: Risk factors for breast cancer for women aged 40 to 49 years: A systematic review and meta-analysis. Annals of Internal Medicine. 2012; 156(9): 635-648.
 Van Ravesteyn NT, Miglioretti DL, Stout NK, et al: Tipping the balance of benefits and harms to favor screening mammography starting at age 40 years: A comparative modeling study of risk. Annals of Internal Medicine. 2012; 156(9): 609-617.
Posted May 3, 2012