Undergoing screening mammography for breast cancer once every two years rather than annually does not increase the risk of advanced-stage or large-size tumors in women aged 50 to 74 years, regardless of their breast density or use of hormone therapy, researchers have determined. 

In 2009, the United States Preventive Services Task Force recommended that women aged 50 to 74 years undergo mammography every two years rather than every one to two years. Yet as Karla Kerlikowske, MD, and colleagues pointed out in their new report for JAMA Internal Medicine, controversy still surrounds the questions of how often a woman should undergo screening mammography and whether screening interval should vary according to risk factors beyond age.

Data were collected from 11,474 women with breast cancer and 922,624 women without the disease. All subjects had undergone mammography from 1994 through 2008. Compared with women aged 50 to 74 years who undergo screening mammography once a year, women in the same age group who have the test once every two years have similar risk of advanced-stage disease and lower risk of false-positive results. The results held even for women who had high breast density or who used hormone therapy. 

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For women aged 40 to 49 years with extremely dense breasts, biennial vs. annual mammography was associated with increased risk of advanced-stage cancer and large tumors. The probability of a false-positive mammography result among women undergoing annual mammography was high among those with extremely dense breasts who were aged 40 to 49 years or who used estrogen plus progesterone. The probability was lower among women aged 50 to 74 years with scattered fibroglandular densities or fatty breasts who underwent biennial or triennial mammography.


  1. Kerlikowske K et al. Jama Intern Med. 2013;173(9):807-816.