Women ages 50 to 74 who undergo mammography screening every other year have a similar risk of advanced-stage disease and a lower cumulative risk of false-positive results than those who get mammograms every year, according to the results of a study published early online in JAMA Internal Medicine.

A mammogram is an X-ray of the breast. Screening mammography is performed in a woman without breast symptoms in order 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. In 2009, the U.S. Preventive Services Task Force (USPSTF) issued guidelines recommending that routine screening of average-risk women begin at age 50 and be performed every two years. A number of other groups, including the American Cancer Society, the American College of Radiology, the American Congress of Obstetricians and Gynecologist, and the American Medical Association, recommend annual screening beginning at age 40.

Currently, mammography is the most reliable tool for screening the general population for breast cancer; however, the screening tool does have its limitations—which can include false-positive test results (a suggestion that cancer may be present when it is not); false-negative results (missed cancers); and overdiagnosis (resulting in unnecessary treatment). Put simply—overdiagnosis is the diagnosis of something that would not have resulted in clinical symptoms in a person’s lifetime.

Because age is not the only risk factor for breast cancer, researchers sought to determine whether the risks and benefits of screening differ according to age, breast density, and postmenopausal hormone therapy use. They analyzed data collected between 1994 and 2008 from the Breast Cancer Surveillance Consortium (BCSC) mammography registries. The study sample included 11,474 women with breast cancer and 922,624 without.

The analysis indicated that biennial versus annual mammography for women ages 50 to 74 was not associated with an increased risk of advanced-stage or large-size tumors regardless of a women’s breast density or hormone therapy use. In contrast, among women ages 40 to 49 with extremely dense breasts, biennial mammography was associated with an increased risk of advanced-stage cancer and large tumors. However, the data also indicated that the cumulative probability of a false-positive result was high among women with extremely dense breasts undergoing annual mammography who were either ages 40 to 49 or who used combination (estrogen plus progesterone) hormone therapy. The risk of false-positives was lower among women ages 50 to 74 with dense breasts who underwent biennial or triennial mammography.

The researchers concluded that women ages 50 to 74 are safe undergoing biennial mammography, regardless of breast density or hormone therapy use because it does not increase the risk of advanced disease, but does substantially reduce the cumulative risk of false-positive results (and subsequent biopsy). In contrast, women ages 40 to 49 with extremely dense breasts should know that annual screening may decrease the risk of advanced-stage disease, but could also result in a higher likelihood of false-positive results.


Kerlikowske K, Zhu W, Hubbard RA, et al. Outcomes of Screening Mammography by Frequency, Breast Density, and Postmenopausal Hormone Therapy. JAMA Internal Medicine. Published early online March 18, 2013. doi:10.1001/jamainternmed.2013.307.

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