This contradicts the most widely cited estimate of 30%, said senior author Ruth Etzioni, a biostatistician and professor in the public health sciences division at Fred Hutchinson Cancer Research Center, in a statement. “While the results confirm that breast cancer over-diagnosis is real, they also reassure that it is not as alarmingly frequent as some studies have suggested.”

Since approximately seven in 1,000 women will be diagnosed with invasive or noninvasive breast cancer via a mammogram, the authors say women should be told that approximately one in 1,000 patients will be found to have a cancer that would never have caused problems. About 60% of the 280,000 cases of breast cancer diagnosed annually in the U.S. are estimated to be made through a mammography screening. As a result, reducing over-diagnosis is expected to spare 25,000 women the costs and risks of unnecessary treatment.


Ryser adds that knowing the benefits and harms of mammography, including over-diagnosis, and having access to high quality evidence is essential to making quality care decisions for screening. "An important step toward effective communication and shared decision making is to reduce uncertainty about the true extent of overdiagnosis. We hope that our estimate of overdiagnosis of 15% among screen-detected breast cancers will reduce uncertainty around the actual frequency of breast cancer overdiagnosis, and will enable physicians and their patients to make more informed decisions around breast cancer screening, follow-up testing, and treatment.

The findings were published in the Annals of Internal Medicine.

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