Adding to the ongoing debate over the benefit of screening mammograms, a new study suggests the tests can reduce breast cancer death rates by 26% in women in their 40s.
The study, whose results were published online by the journal Cancer and will be presented Friday at the yearly American Society for Clinical Oncology conference, compared 24 years of breast cancer mortality data from Swedish counties that invited women in their 40s to get mammograms and counties that did not. They found that breast cancer death rates in counties with screening were 26% lower than in counties without. (More on Time.com: Clinical Trial Dilemma: Save Lives Now — or Later?)
The findings counter the 2009 U.S. Preventive Services Task Force (USPSTF) guidelines for American women, which recommend against routine mammogram screening in women in their 40s. A Norwegian study released Sept. 22 by The New England Journal of Medicine also found a small reduction in breast cancer death risk in women who were being screened, but concluded that the actual reduction attributable to mammograms was just 10%. That study focused on women over 50, however.
The new study has critics. As the New York Times reports:
One problem, said Dr. Peter C. Gotzsche of the Nordic Cochrane Center in Copenhagen, a nonprofit group that reviews health care research, is that the investigators counted the number of women who received a diagnosis of breast cancer and also died of it. They did not compare the broader breast cancer death rates in the counties.
It is an important distinction, Dr. Gotzsche said, because screening finds many cancers that do not need to be treated or found early. With more harmless cancers being found in the screened group, it will look like the chance of surviving breast cancer is greater in that group. “The analysis is flawed,” he said.
Indeed, there is little disagreement that overdiagnosis can be harmful to patients and costly to the health-care system. In April, Dartmouth researchers published a review of the impact of such hyper-vigilance in the Journal of the National Cancer Institute.
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