NEW research published in the JAMA Internal Medicine journal suggests that mammograms reduce the risk of breast cancer-related deaths by 10 percent, rather than the original 20 to 25 percent. The analysis signals “widespread overdiagnosis” in US women, researchers say.

The study examined the relationship between screening rates in US communities and breast cancer death rates and tumor sizes.

Tracking 16 million women ages 40 and older in 547 counties, 53,207 of those followed were diagnosed with breast cancer in 2000. In April, the US Preventive Services Task Force issued new recommendations that women get mammograms every two years once they turn 50—compared with its previous guidance that women ages 40 and up get mammograms every one to two years.

The study authors found that mammograms resulted in an increased diagnosis of small tumors, but not a decreased diagnosis of larger tumors or change in the death rate.

“Our analysis shows that, when directed toward the general US population, the most prominent effect of screening mammography is overdiagnosis,” the authors wrote.

They encourage further research into whether all women who undergo a mammogram have the same risk for overdiagnosis, or if the diagnosis is more likely in certain age or ethnic groups.

“Overdiagnosis” relates to detection of a tumor that would have gone unnoticed without mammography. The risk of overdiagnosis is that women whose tumors are not life-threatening could be subjected to harm in the form of unnecessary treatment and undue anxiety, according to Dr. Joann Elmore from the University of Washington School of Medicine.

“We need clear communication and better tools to help women make informed decisions regarding breast cancer screening mammography,” Elmore wrote. (With reports from US News & World Report)