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Breast Cancer Health Center

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Mammograms Spot Cancers That May Not Be Dangerous

As Many as 25% of Cancers Detected by Mammograms May Be Overdiagnosed, Study Finds

Estimating Overdiagnosis in Breast Cancer continued...

“What women have been told before is, ‘You look for cancer and we’ll save you,’” says researcher Mette Kalager, MD, a breast cancer surgeon and an epidemiologist with the Harvard School of Public Health. “That’s not the whole story. You will be saved without screening as well.”

“I think we have to inform women about the downside or harm of mammography screening,” she says.

The study is published in the Annals of Internal Medicine.

The number of women who are overdiagnosed in the U.S. is likely to be higher, experts say, because women in this country often start getting mammograms in their 40s, rather than in their 50s as women in Norway do, and Americans are generally screened more often, every year instead of every two years.

“If you’re starting in the U.S. at a younger age, and you’re doing screening more frequently, that means you have more chances to be screened, and every time you’re screened you’re at risk of overdiagnosis,” says Joann G. Elmore, MD, MPH, a professor of medicine at the University of Washington in Seattle.

Elmore wrote an editorial on the study, but she was not involved in the research.

She says previous studies have shown that radiologists in the U.S. have about a 10% recall rate; that is, they call about 10% of women back for more testing because they’re worried about something they see on the X-ray. In other countries, radiologists have about a 2% recall rate. That higher index of suspicion also raises the likelihood of overdiagnosis.

Weighing the Benefits and Harms of Mammograms

Overdiagnosis, it should be noted, is not the same thing as another risk of cancer screening tests: false-positive results. A false-positive is a result that looks suspicious and may lead to more testing, but the patient is ultimately cleared of cancer.

“That test is eventually shown not to be cancer, but in the time it takes to figure that out, women are made anxious, many are never totally relieved,” says H. Gilbert Welch, MD, MPH, a professor of family and community medicine at Dartmouth Medical School in Hanover, N.H.

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