Are Mammograms Overdiagnosing Breast Cancer?
A new study finds that while mammograms detect more early-stage breast cancers, they have only a small impact on reducing cancer deaths.
--by Suzanne Boothby
For the past 30 years, the medical community has promoted early detection of breast cancer through screening as one of the best ways to reduce the number of deaths from breast cancer. But a new study says the impact has not been as effective as once hoped.
The latest research published in The New England Journal of Medicine found that mammogram screenings account for nearly a third of all newly diagnosed breast cancers, but that screening has only a small effect on the rate of death from breast cancer.
Early detection can lead to earlier treatment and help head off the cancer before it spreads. But it can also result in over-diagnosis and over-treatment, which exposes more women to the adverse effects of cancer therapy.
“We estimate that breast cancer was over-diagnosed (i.e., tumors were detected on screening that would never have led to clinical symptoms) in 1.3 million U.S. women in the past 30 years,” the study authors wrote.
In 2008, breast cancer was over-diagnosed in more than 70,000 women, accounting for 31 percent of all breast cancers diagnosed, according to the study.
The Expert Take
“Breast cancer over-diagnosis is a complex and sometimes contentious issue,” study authors Archie Bleyer, M.D., and H. Gilbert Welch, M.D., M.P.H. wrote. “Ideally, reliable estimates about the magnitude of over-diagnosis would come from long-term follow-up after a randomized trial.”
Still, their study raises questions about the value of mammography screening.
“It clarifies that the benefit of mortality reduction is probably smaller, and the harm of over-diagnosis probably larger, than has been previously recognized,” they wrote.
Source and Method
Researchers examined screening mammography in women 40 years old and older using available national data. They incorporated surveillance, epidemiology, and end results data to examine trends from 1976 through 2008 in the incidence of early-stage breast cancer and late-stage breast cancer.
The researchers found substantial over-diagnosis of breast cancer and only a small reduction in the rate of death from breast cancer since mammograms were first introduced. The authors said their study does not answer the question of whether or not women should be screened for breast cancer, but it does invite further study.
The National Cancer Institute recommends that women ages 40 and older should have a mammogram every one to two years, and women with a higher than average risk of cancer should talk to their health care providers about when to begin screening and how often to get tested.
A 2011 study in Norway examined the effect of mammography screening on surgical treatment for breast cancer and found that screening was associated with a noticeable increase in rates of breast cancer surgery in women ages 50 to 69.
A comprehensive Swedish study, also published in 2011, found that mammography screening for women ages 40 to 49 was effective at reducing breast cancer mortality.