US Pharm. 2011;36(Oncology/Hematology suppl):14.

One in two healthy women who have an annual mammogram will get at least one false-positive result over a 10-year period, and 7% to 9% will undergo a biopsy that does not ultimately reveal cancer, according to researchers from the Group Health Center for Health Studies in Seattle, Washington. Having a mammogram every other year instead of every year would cut the risk of a false positive by about a third, but it could result in catching cancers at a later stage, they report in the Annals of Internal Medicine. In the latest study, the researchers analyzed data from a large breast cancer registry that included more than 169,000 women aged 40 to 59 years  in seven regions around the U.S. 

In 2009, the U.S. Preventive Services Task Force issued new guidelines that suggested women should start routine mammograms at age 50 years rather than 40 years, in part because the tests have such high false-positive rates and the benefits in lives saved did not outweigh the worry and anguish caused by the false-positive results. Many groups, including the American Cancer Society, have stuck by their long-standing recommendations of a yearly breast exam for women starting at age 40 years, stressing that the breast x-rays have been proven to save lives by spotting tumors early, when they are most easily treated.