Women should understand these risks, Visco said. Instead, women often hear only about mammograms’ benefits.

“Women have been inundated with the early detection message for decades,” Visco said.


The risks of overdiagnosis and false positives, which can lead women with benign growths to undergo biopsies and other follow-up tests, have caused some experts to reevaluate breast cancer screenings. Although mammograms don’t find all tumors, they reduce the risk of dying from breast cancer by 25 percent to 31 percent for women ages 40 to 69, according to the Agency for Healthcare Research and Quality, part of the Department of Health and Human Services.

Medical groups now offer differing advice on mammograms:

The American College of Radiology takes the most aggressive stance, recommending annual mammograms beginning at age 40. Tumors should be found when they’re “smaller and easier to treat,” Monticciolo said.

The U.S. Preventive Services Task Force, an independent expert panel that advises the federal government on health, provoked a firestorm of criticism in 2009 when it bucked that advice, recommending that women get mammograms every other year beginning at age 50. The group noted that breast cancer risk rises with age, so mammograms are more likely to discover cancer – as opposed to benign growths – after age 50.

The American Cancer Society also scaled back its screening advice in 2015, recommending women get annual mammograms from 45 to 54, followed by screenings every other year after that.

In the new study, Danish researchers estimated the rate of overdiagnosis by comparing the number of early-stage and advanced breast tumors before and after the country started offering mammograms. If screenings work as intended, the number of small, curable breast tumors should increase, while reducing the number of large cancers by about the same amount.

Although mammograms in Denmark detected a lot more breast cancers, these were mostly small, early-stage tumors, said study coauthor Dr. Karsten Jorgensen, a researcher at the Nordic Cochrane Center in Copenhagen, Denmark. The number of advanced cancers did not fall.

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