Study quantifies risk of false positives with annual mammograms

More than half of healthy women who receive an annual mammogram will experience at least one false-positive result over 10 years, according to a study in the Annals of Internal Medicine.

Researchers led by the Group Health Research Institute in Seattle reviewed medical records from more than 169,000 women ages 40 to 59. Across a decade of annual screening, 61% of participants received a false positive and were called back for additional screening, and about one in 12 women were called in for a biopsy that later turned out to be non-cancerous.

When women were screened every other year, the probability of receiving a false positive dropped to 42%. Women who received biennial screenings were not significantly more likely to be diagnosed with late-stage cancer compared with women screened annually. In addition, the researchers said women had a similar risk of having a false positive in their 40s and 50s, but women who started having annual mammograms at age 40 would have more false positives over their lifetimes because of the extra decade of screening.

The results support 2009 guidelines from the U.S. Preventive Services Task Force that recommended women receive mammograms every other year starting at age 50, in part because the potential negative effects of false positives outweigh the benefits of more frequent screening. The guidelines triggered a backlash from some advocacy groups who maintain that frequent mammograms save lives.

Study author Rebecca Hubbard said physicians should use the findings to help patients make informed decisions about mammograms in a way that minimizes anxiety. "I think it gives us quantification of risks and benefits, so when individuals consider how frequently to screen they can think of what their risk of cancer is and what their risk tolerance is for potentially getting a false positive," Hubbard said (Steenhuysen, Reuters, 10/17; Fox, National Journal, 10/17 [subscription required]; Roan, "Booster Shots," Los Angeles Times, 10/17).

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