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Routine mammography's potential harm: Overdiagnosis

Researchers at the Harvard School of Public Health estimate that for every 2,500 women invited to screening, only one life will be saved.

Routine mammography screening, widely considered crucial in early breast cancer detection, may in fact be doing its job too well.

Harvard School of Public Health

It turns out that as many as a quarter of the early cancers detected by mammography would not progress. That suggests early detection results in a great deal of unnecessary treatment and stress, according to a Harvard School of Public Health analysis of a nationwide screening program in Norway.

"Radiologists have been trained to find even the smallest of tumors in a bid to detect as many cancers as possible to be able to cure breast cancer," lead author and visiting scientist Mete Kalager said in a school news release. "The present study adds to the increasing body of evidence that this practice has caused a problem for women -- diagnosis of breast cancer that wouldn't cause symptoms or death."

The researchers, whose findings appear this week in the Annals of Internal Medicine, had at their disposal a wealth of data from the Norwegian Breast Cancer Screening Program, launched in 1996 for women ages 50 to 69. Nearly 40,000 women participated in the program, one in five of whom were diagnosed with some form of breast cancer.

But of the 7,793 women diagnosed through the program, as many as 25 percent (1,948) were overdiagnosed. The team goes on to estimate that for every 2,500 women invited to screening, only one life will be saved, while 6 to 10 women will undergo unnecessary treatment for a cancer that never would have progressed.

Put another way, regular mammography screening may result in 6 to 10 women undergoing great physical and emotional stress in order to save one life.

What's more, the team at Harvard found no reduction in late-stage disease in women who'd been offered screening, suggesting that early detection through mammography may not be as helpful in preventing late-stage cancer as previously thought.

The findings join a growing body of evidence that regular mammography screenings help only a tiny fraction of women diagnosed with breast cancer, as the majority of cases are caught early enough to result in overdiagnosis or late enough to render treatment useless.

What to do with these findings? For now, Kalager says, women should be better informed about the potential harms of regular screening, from unnecessary surgeries and treatments to emotional distress, so that they may weigh them against what increasingly look like limited potential benefits.