Mammograms Spot Cancers That May Not Be Dangerous
As Many as 25% of Cancers Detected by Mammograms May Be Overdiagnosed, Study Finds
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Estimating Overdiagnosis in Breast Cancer continued...
“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.
Arguably, Welch says, overdiagnosis is even more insidious.
“You’re treated for a breast cancer that was never going to bother you. Now you’re talking about real intervention. Mastectomy, lumpectomy, surgery, radiation,” he says.
Not to mention the mental toll of a cancer diagnosis.
Welch points to the fact that for every 2,500 women screened for a decade with regular mammograms, one life will be saved thanks to early detection.
But, he says, “It’s very relevant what happens to the other 2,499 women. In this country, somewhere around 1,000 will have at least one false-positive result and about half will have a biopsy, so that’s a lot of angst there.”
Based on this study and several others, Welch says it looks like “somewhere between five and 15 will be overdiagnosed to receive unnecessary treatment for cancer.”
“We need to work to make the deal better for patients,” Welch says. “There might be reasons to screen less often, look less hard, stop screening earlier.”
To Screen or Not to Screen?
To try to reduce some of the harms associated with screening, in 2009, the U.S. Preventive Services Task Force changed its recommendations for routine mammograms, saying women should get one every two years starting at age 50, rather than every year beginning at age 40.
Those recommendations, however, are at odds with guidelines from other groups, including the American Cancer Society and the American College of Radiology, who say screening should start at age 40 or even younger for high-risk women.
For women who are weighing the risks and benefits of getting regular mammograms, Welch says he advises patients to remember that cancer screening is a choice made after consultation with your doctor regarding risks and benefits of screening.