Screening this postmenopausal age group for a decade reduced breast cancer deaths by a "modest" 10 percent, which translates to one life saved per 2,500 women who got the breast X-rays, according to the analysis of Norway's cancer registry. Previous studies have estimated this "mortality benefit" to be about 25 percent.
The new study did not look at the risks of screening - namely, overdiagnosis and overtreatment. However, the editorial said that in the United States, about 1,000 of every 2,500 women screened for a decade would have at least one false alarm, 500 of them would undergo an unnecessary biopsy, and five or more would be treated for cancers that would never have become lethal.
"The test is surely a close call, a delicate balance between modest benefit and modest harm," H. Gilbert Welch, a Dartmouth Medical School primary-care physician, wrote in his editorial.
That message could be misinterpreted, worried Emily F. Conant, chief of breast imaging at the Hospital of the University of Pennsylvania.
"Women are looking for reasons not to get their mammograms," Conant said. "We know mammography works. To cut back now, when we know how to hone and make it even better, is going back in time." Ultrasound, MRI imaging, and digital technology are now used to clarify ambiguous mammograms.
Much of the mammography debate rests on now-outdated studies done from the 1960s through the 1980s in which women were randomly assigned to get mammograms or not.
