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Are Benefits of Annual Mammograms Overstated?

Analysis of 50 years of clinical data adds to controversy over who should be screened, how often

WebMD News from HealthDay

By Amy Norton

HealthDay Reporter

TUESDAY, April 1, 2014 (HealthDay News) -- The benefits of mammography screening are probably oversold, while the risks -- especially "overdiagnosis" -- are underappreciated, a new review concludes.

The report, published in the April 2 issue of the Journal of the American Medical Association, adds to the controversy that's been building in recent years over the value of mammography screening. In this latest finding, data from 50 years of research was analyzed.

In 2009, the U.S. Preventive Services Task Force (USPSTF) caused a stir when it changed its recommendations on mammograms, which had long advised women to have one every one to two years, starting at age 40.

The revised guidelines now say routine screening should begin at age 50, and be done every two years. If a woman wants to begin screening in her 40s, the task force suggests she discuss the pros and cons with her doctor.

The changes came in response to growing evidence that for women in their 40s, there is only a small "net benefit" from mammography screening. And the new findings show more of the same.

Researchers found that, based on clinical trials done since the 1960s, mammograms can save lives, but the effects are small for women in their 40s: Screening cuts the risk of death from breast cancer by an average of 15 percent in this age group.

And that small benefit has to be weighed against the risks of screening, said review co-author Dr. Nancy Keating.

The risk that concerns Keating the most is "overdiagnosis" -- where women with tumors that would never have threatened their lives go through needless surgery, chemotherapy and radiation.

Experts now know that some breast cancers never progress to the point where a lump would be felt, or even go away on their own. But with screening, those cancers are detected and treated.

"We have no way of knowing which patients will progress," said Keating, of Harvard Medical School and Brigham & Women's Hospital in Boston. "So we have to treat everyone we diagnose."

It's hard to estimate the number of women who are overdiagnosed with breast cancer, Keating said. But based on the studies her team reviewed, a "best estimate" is that 19 percent of cancers diagnosed over 10 years of screening are actually overdiagnoses.

"We think mammography has a benefit," Keating said, "but it's smaller than many people believe. And the risk of overdiagnosis, in particular, has not received a lot of attention."

Older women, who have a higher rate of breast cancer, see more benefits from screening, the review found: For those in their 60s, mammograms reduce the risk of breast cancer death by one-third.

One cancer expert said the estimates sound about right.

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