Study Questions Benefits of Mammogram Screening

More than one million U.S. women have been diagnosed and treated unnecessarily for breast cancer in the 30 years since screening mammograms become widespread, according to a study in the New England Journal of Medicine.

In 2008, the most recent year studied, nearly 1 in every 3 breast cancers were "overdiagnosed"—that is, they never would have caused symptoms if they had been left alone, the study concluded.

The findings add to the growing body of evidence that suggests screening women for breast cancer leads to unnecessary treatment while saving few lives, likely fueling the controversy about when and how often to have regular mammograms. Previous studies, many comparing populations in Europe, have estimated the overdiagnosis rate at 15% to 50%.

Doctors still can't tell which breast cancers are destined to be deadly and which can safely go untreated. The estimates are from statistical analyses and are based on the idea that screening saves lives only if it increases the number of cancers detected at early, treatable stages and decreases those found later, when treatment is less-effective.

The new study found that early-stage breast cancers diagnosed annually in the U.S. doubled—to 234 from 112 per 100,000 women—between 1976 and 2008, but late-stage breast cancers fell by only 8 per 100,000 women in the same period.

"It looks like the primary effect of screening has been to tell a whole lot more women that they have early-stage disease" and incurring unnecessary surgery, radiation and chemotherapy, said study co-author H. Gilbert Welch, a professor of medicine with the Dartmouth Institute for Health Policy and Clinical Practice. The axiom that early detection saves lives only applies if those cancers were destined to progress, he adds.

Overall deaths from breast cancer for women over age 40 dropped by 28% in the past 30 years, but the study's authors attribute that more to improved treatment than early detection, in part because the death rate among women under 40 dropped even further, even though very few women that age are screened.

The study used data from the Center for Disease Control and Prevention's National Health Interview Survey and from the federal Surveillance, Epidemiology and End Results Program.

Other cancer experts agree that overdiagnosis exists, but some contend that screening saves lives, on balance. "We have eight prospective, randomized trials that show that screening and treatment decrease the relative risk of death by 15% among women in their 40s and up to 30% among women in their 60s," said Otis Brawley, chief medical and scientific officer of the American Cancer Society.

The group recommends that women have annual mammograms starting at age 40, even though the U.S. Preventive Task Force since 2009 has urged women to get mammograms only every other year starting at age 50.

Scientists are working on ways to distinguish between cancers that are fast-moving and lethal from those that are slow-growing. In breast cancer, tests such as Oncotype DX or MammaPrint can predict how individual tumors are likely to behave, and can advise patients whether they are likely to benefit from chemotherapy in addition to radiation and surgery.

"We are not yet at the point where we can say, 'We see your cancer and we don't need to take it out,' " but that may be coming, says Laura Esserman, director of the Carol Franc Buck Breast Cancer Center at the University of California, San Francisco, who wasn't involved in the current study.

In the meantime, Dr. Esserman says, "The good news is that if you are diagnosed with cancer, don't panic—it may not require a lot of treatment. Make sure you ask your doctor about your options."

By: Melinda Beck, Wall Street Journal
Posted by: Scott W. Yates, MD, MBA, MS, FACP

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