Controversial U.S. guidelines for mammography issued in 2009, calling for screening every two years rather than annually for women over 50 years old, can result in breast cancers being missed, according to U.S. researchers studying the hotly debated topic.

This latest study assessing the impact of revised guidelines issued by the U.S. Preventive Services Task Force three years ago comes on the back of a chilling analysis published last week in the New England Journal of Medicine (NEJM).

The NEJM study, using three decades of U.S. government data, found that nearly one in three patients - or 1.3 million women - whose cancer was detected through routine mammograms was treated for a tumor that may not have been life threatening.

Routine screening has traditionally been recommended by the task force and the American Cancer Society for all women over the age of 40. The American Cancer Society has not changed its stance, but the task force issued new guidelines in 2009, recommending mammography every two years for women 50 to 74 years old.

Dr. Elizabeth Arleo of Weill Medical College of Cornell University and lead researcher examined the impact of the revised task force guidelines on women 40 to 49 years of age and 65 years and older.

Arleo analyzed data on screening mammography at New York Presbyterian Hospital/Weill Cornell Medical Center between 2007 and 2010. Over those four years, 43,351 mammograms were performed, leading to the detection of 205 breast cancers. Nearly 20 percent of cancers detected with screening mammography were found in women in their 40s.

“In our book, it seems unacceptable to miss 19 percent of breast cancers, half of which were invasive,” she said, noting that “invasive” cancers are more advanced because they reside in the breast tissues and not just the breast ducts.

“Our findings favor the American Cancer Society recommendations. Women over 40 should have annual mammograms. In my book, there’s no confusion. I tell my patients, I tell my friends, and I tell my mother to get annual mammograms,” Arleo said in a telephone interview. “We hope we can quell some of the confusion.”

She presented her findings at the Radiological Society of North America meeting in Chicago.

Arleo dismissed the NEJM analysis, calling the premise and conclusions of the analysis flawed, mostly because no one can say for sure which cancers would have progressed to an advanced or life-threatening state.

“We need to understand the biology of cancer so we know which cancers to treat. Until that question is answered, screening is our best shot,” she said.

She acknowledged that false positives are a problem of widespread screening.

“But for every test, you have to do a risk-benefit analysis, not just for mammography,” Arleo added.

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Reuters