What benefits do women really get from mammograms?

Here’s a story you’ve probably heard before: A middle-age woman walks in for a yearly screening mammogram, gets diagnosed with an early-stage breast cancer and 20 years later tells everyone the mammogram saved her life. While that scenario certainly seems to make sense, mammograms only provide lifesaving benefits to about one in five women whose breast cancers are detected via the screening X-ray, according to a study published yesterday in the Archives of Internal Medicine.

The general perception is that 100 percent of women who have their breast cancers diagnosed thanks to a mammogram will benefit from the screening, said study author Dr. H. Gilbert Welch, a professor of medicine at the Dartmouth Institute for Health Policy & Clinical Practice. “If we believe every breast cancer survivor benefits from mammograms, it becomes a powerful incentive for us to diagnose more and more breast cancers, and that can lead to overdiagnoses.’’


In the study, Welch used a government software system to calculate the average 50-year-old woman’s risk of having breast cancer detected on an annual mammogram over the next 10 years to be about 2 percent and her risk of dying from that cancer to be about 1 percent. If she hadn’t had a mammogram, she would have had about a 1.2 percent chance of dying from breast cancer.

From this data, the researchers calculated that just 13 to 17 percent of breast cancer patients whose cancers were detected on mammograms actually reaped lifesaving benefits from the screening. (That was assuming that yearly mammograms reduced a woman’s risk of dying from breast cancer by 20 to 25 percent; Welch said more recent studies indicate the lifesaving benefits may be more along the lines of 10 to 15 percent.)

While these calculations may seem confusing, they do highlight an important message: Mammograms certainly save women’s lives but they don’t save the life of every woman whose cancer is found on the X-ray. Some may have slow-growing non-aggressive malignancies that might have never become life-threatening — or may have even disappeared altogether before growing into a lump that could be felt by the woman. Others may have deadly cancers that grow and spread rapidly in between the annual screenings.

Welch said he’d like to see doctors only perform biopsies on suspicious growths detected on mammograms that are larger than 1 centimeter. This, he believes, could cut down on the number of women diagnosed with minute malignant growths that don’t need to be treated.

That view, though, is controversial and studies would need to ascertain that this approach wouldn’t lead to more breast cancer deaths.

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