'Substantial overdiagnosis' of breast cancer blamed on screening mammos

The issue of screening mammography and overdiagnosis of breast cancer once again is roiling the radiology community.

An article published Nov. 22 in the New England Journal of Medicine has concluded that screening mammography has "only marginally" reduced the rate at which women present with advanced cancer, and has led to substantial overdiagnosis of the disease.

The article was quickly challenged, according to Diagnostic Imaging, by the American College of Radiology, which released a statement calling the study "deeply flawed and misleading."

The authors of the NEJM article--Gilbert Welch, M.D., M.P.H., of the Dartmouth Institute for Health Policy and Clinical Practice in Lebanon, N.H., and Archie Bleyer, M.D., of the St. Charles Health System in Bend, Ore.--used Surveillance, Epidemiology, and End Results data from 1976 through 2008 to examine trends in the incidence of early- and late-stage breast cancer in women over 40. They determined that screening doubled the number of women diagnosed with early-stage cancer, from 112 to 234 cases per 100,000 women--an increase of 122 cases per year. At the same time women presenting with late-stage cancer decreased from 102 to 94 cases per year, a decrease of eight per 100,000 women.

"With the assumption of a constant underlying disease burden, only eight of the 122 additional early-stage cancers diagnosed were expected to progress to advanced disease," Welch and Bleyer wrote.

After excluding the transient excess incidence associated with hormone-replacement therapy and adjusting for trends in the incidence of breast cancer among women younger than 40 years of age, Welch and Bleyer concluded breast cancer was overdiagnosed in 1.3 women over the last 30 years, including more than 70,000 women in 2008 alone.

"We've suggested to women that having a mammogram is one of the most important things you can do for your health, and that's simply not true," Welch told the Ithaca Journal. "I can't tell you the right thing to do, except to tell women the truth, tell them both sides of the story. We shouldn't be scaring women. This is a really close call."

According to the Diagnostic Imaging article, ACR said that numbers used by Welch and Bleyer were incorrectly determined.

Barbara Monsees, chairwoman of the ACR's Breast Imaging Commission and a professor of radiology at Washington University in St. Louis told Bloomberg that looking at trends of advanced cancer in proportion to other stages of cancer is not enough to determine whether mammograms are saving lives.

"At this point in time we really don't have a choice anyway," Monsees said. "It's not the fault of screening that we're finding cancers that may not advance and kill people. Right now we don't know how to differentiate those cancers from other cancers, the killing cancers, basically we're treating them all the same. I don't think it should stand in the way of women getting screened."

For more information:
- read the New England Journal of Medicine article
- see the article in Diagnostic Imaging
- read the article in  the Ithaca Journal
- read the article on Bloomberg

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