By Joe Elia
Annual mammography screening in women under age 60 does not confer a breast cancer mortality advantage, and it results in more than 20% overdiagnosis among the lesions found, according to a follow-up of the Canadian National Breast Screening Study.
As reported in BMJ, between 1980 and 1985, some 90,000 women aged 40 to 59 were randomized to 5 years of annual mammography or no mammography (women aged 40-49 in the mammography group and all women aged 50-59 received annual physical breast examinations).
After up to 25 years' follow-up, there was no discernible difference between groups in breast cancer mortality. Of the screen-detected tumors, 22% were overdiagnoses — one for every 424 women in the mammography arm.
Andrew Kaunitz, an OB/GYN with NEJM Journal Watch, comments: "This important Canadian report documents the failure of screening mammography to impact mortality from breast cancer, as well as breast cancer overdiagnosis. Based on these and other recently published data, clinicians and women should move away from starting screens among women in their 40s and from screening annually. While we reevaluate the practice of screening mammography, adopting the U.S. Preventive Services Task Force 2009 recommendations (beginning screening in average-risk women at age 50 and screening biennially) would appear prudent."
Medicine has a precedent of handling predictive tests poorly. Consider the PSA test, which detects a protein linked to prostate cancer. Not only does the test produce false positives a majority of the time, but some of the tumors it actually detects are so slow-growing that they aren’t worth treating. Millions of men have ended up getting treated for cancers that ultimately wouldn’t have affected them. By one estimate, for every 47 men who had their prostates removed, a single cancer death was avoided. Studies by researchers at Dartmouth College suggest that mammography also leads to overdiagnosis and overtreatment. About 25 percent of breast cancers discovered, and treated, would not have caused any symptoms. “You test everyone and end up treating people for diseases that would never have mattered, either because they wouldn’t have progressed or because people die of something else,” says Jonathan Skinner, a health economist at Dartmouth. “The downside of early screening can be very high.”
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