"Mammography is not perfect; no one has claimed that it is," said Kopans, a member of the ACR Commission on Breast Imaging. But since the advent of routine mammograms in the 1990s, the rate of death from breast cancer has dropped 30 percent, he observed.
"That's a huge achievement," Kopans noted, adding that "it may not be a big deal to an epidemiologist who's looking at huge numbers and doesn't take care of women with breast problems."
Norway's breast cancer screening program began in 1996 and was expanded two years later, with staggered enrollment by county over a period of nine years. Since 2005, all Norwegian women aged 50 to 69 have been invited to have a screening mammogram every two years, the authors said.
For the study, more than 40,000 Norwegian women were followed for an average of 2.2 years. Researchers compared death rates from breast cancer among four groups of women: two that were living in counties with or without screening and two groups that lived in the same counties before screening was offered.
The difference in the rate of death from breast cancer among women in the screening group versus the control group was 28 percent. In comparison, there was an 18 percent reduction in the rate of death in the non-screened group versus the control group, the study found.
In other words, breast cancer screening was associated with a reduction in death -- but only accounted for 10 percentage points of the difference.
"Our observed 10 percent reduction in death from breast cancer is much lower than previously thought," Kalager said. "It is plausible that today, the effect of increased breast awareness and improved therapy have outweighed the effect of screening on reducing mortality from breast cancer."<
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