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The American Cancer Society has finally done what no other American medical professional society dealing with breast cancer has been willing to do — examine the available evidence and recommend that mammogram screening start later and be performed less frequently. The response from politicians, the media and some physicians was swift, predictable and misguided.

For years the United States, in accordance with recommendations from the cancer society and other medical societies, has been the only country to recommend annual mammography screening for breast cancer starting at age 40 — other countries start mammography at 50 and then test every two to three years up to ages between 70 and 74.

The U.S. Preventive Services Task Force, a respected, independent panel of primary care and preventive medicine experts, reviewed the risks and benefits of mammography in 2009 and again in 2015. Both times it advised that mammography no longer be routinely recommended for average-risk women in the 40-49 year old age group because the risks outweigh the benefits. Instead, the USPSTF recommended that women between 50 and 74 have mammograms every other year rather than annually.

Both times the suggestion was immediately condemned by medical groups, patient groups and politicians from both parties.

Advocates emphasize the benefits of screening. But deciding when to start the tests and how often to screen are important to limit the potential harms from screening. Over a 10-year period, women who are screened annually have a 61.3 percent probability of having at least one false positive result.

False positives are more common in younger women and the number of false positives rises with the number of screens performed. Each false positive leads to additional X-rays, anxiety and, for 10 percent to 20 percent of false positives, an unnecessary biopsy. Biennial screening reduces the probability of a false positive by a third.

Starting later reduces the lifetime number of mammograms. Screening also risks overdiagnosis — finding an early cancer that would never cause symptoms or threaten the woman’s life. The best estimates of mammography overdiagnosis range between 19 percent and 31 percent. Each overdiagnosed cancer is treated with a combination of surgery, radiotherapy and toxic chemotherapy, forcing women to bear the physical and emotional scars of unnecessary treatment.

A recent study in Health Affairs found that overdiagnosis and false positives in women 40 to 59 years old cost $4 billion — i.e., half of the annual mammography screening expenditure.

After a two-year review, the American Cancer Society changed its longstanding advice to start annual mammograms at 40 and recommended starting annual screening at 45, switching to biennial screening for women between 55 and 70 and continuing biennial mammograms for women over 70 who remain in good health.

The new cancer society guidelines are a step in the right direction. They acknowledge that early, frequent screening does not necessarily save lives and subjects many women to unnecessary treatment. The $4 billion expended annually on overdiagnosis and false positives would be better spent on treatment and on research to determine which detected cancers are truly dangerous and need treatment, and which can be left alone.

Joel Zinberg is a surgeon at Mount Sinai Hospital in New York and an associate clinical professor of surgery at the Icahn School of Medicine. He is also a visiting scholar at the American Enterprise Institute.

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