WASHINGTON, July 7 (UPI) -- Screening mammography in the United States has resulted in the discovery of more small cancers, however the increase in scans has not resulted in a decrease of the risk of dying from breast cancer.
Rather than saving lives, researchers found in a new study that the main result of an increase in mammograms over the course of a decade was over-diagnosis and possibly harm.
"This study shows that the more we look, the more you find," Joann Elmore, a professor of medicine at the University of Washington, told NPR. "The more you screen, the more likely you are to detect early precancerous abnormalities like ductal carcinoma in situ and early-stage cancer."
Researchers reviewed the records of 16 million women at least 40 years old who underwent breast cancer screening in 547 counties during the year 2000. They found 53,207 women who were diagnosed with breast cancer and whose progress was tracked from their initial diagnosis in 2000 until December 2010.
The data showed that increased screening revealed 16 percent more cancers being found overall, however the breast cancer death rate remained unchanged. When considering for size of the tumors found, researchers said 25 percent more small tumors were found and 7 percent more large ones were discovered.
While other studies have shown a 20 percent reduction in breast cancer deaths, researchers said mortality from breast cancer alone may be too rare to reliably detect with their study. They note, however, that the increase in mammograms has not reduced the number of large tumors found. Rather, it shows a lot more small tumors are being discovered with a negligible number of lives being saved.
"Treatment of an overdiagnosed tumor cannot provide benefit, but it can lead to harm," Elmore wrote in an editorial published alongside the study. "Overdiagnosis and overtreatment are now widely acknowledged to be an important harm of medical practice, including cancer screening."
The conclusion of both researchers and Elmore is that widespread screening mammography has not saved additional lives and, based on other studies, may be harming women because of the process of a mammogram and stress associated with awaiting its results.
"We do not believe that the right rate of screening mammography is zero," researchers wrote. "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."
The study is published in JAMA Internal Medicine.