The importance of regular mammograms to ending breast cancer has been widely endorsed by everyone from a government-backed panel to patient advocacy groups and Angelina Jolie. Is it possible they've all been wrong?
A new study in JAMA Internal Medicine published Monday looked at data from 16 million women in 547 U.S. counties in 2000. More than 53,000 were diagnosed with breast cancer that year. As expected, the researchers found that the number of breast cancer diagnoses rose with more aggressive screenings. The surprise: the number of deaths remained the same.
The study found that mammography resulted in diagnosis of additional small cancers, but was not associated with higher detection of more advanced and dangerous larger tumors. The researchers -- including Richard Wilson, a professor at Harvard University who has been conducting a series of studies on risk-benefit analysis and cancer -- argued that these findings "suggest widespread overdiagnosis."
The issue of overdiagnosis (and overtreatment) in cancer care -- not just in breast cancer but also in cancers of other regions of the body such as the prostate and lungs -- has prompted heated debate in recent years. One big issue in breast cancer specifically is the number of false positives in mammograms, which are estimated to be anywhere from less than 10 to 50 percent of all women who are screened. In an opinion piece accompanying the Wilson study, researchers from the University of Washington School of Medicine expressed concern that that this lack of clarity has left both patients and their caregivers in a conundrum.
"Treatment of an overdiagnosed tumor cannot provide benefit, but it can lead to harm. Overdiagnosis and overtreatment are now widely acknowledged to be an important harm of medical practice, including cancer screening," Joann G. Elmore and Ruth Etzioni wrote.
Just last month, researchers from the University of Copenhagen warned of the psychological strain of false-positive mammograms in a study in the journal Annals of Family Medicine. They found that even when women are told that the initial diagnosis was wrong, they still show signs of stress and depression several years later.
So what does all this mean for women concerned about breast cancer? Wilson and his co-authors said that their study is vulnerable to what they called "ecological biases" wherein conclusions about individuals are drawn from data about groups, and Elmore and Etzioni agree that there may be other explanations for the relationship between screenings and incidence of mortality.
Meanwhile, the study authors' advice is that they don't believe "the right rate of screening mammography is zero," but they don't state much beyond that.
"As is the case with screening in general, the balance of benefits and harms is likely to be most favorable when screening is directed to those at high risk, provided neither too frequently nor too rarely, and sometimes followed by watchful waiting instead of immediate active treatment," they wrote.
Current guidelines from the U.S. Preventive Services Task Force recommend screening every two years for women ages 50 to 74 and that those who are younger should also consider screening depending on individual risk factors, such as family history of the disease.