The trials compared women in their 40s who received mammograms with women who didn't. Altogether, these trials enrolled 200,000 women in the United States, Canada, Scotland and Sweden. When considered together in a meta-analysis, the studies conclude that approximately15 years after the trials ended, women who were screened had 18 percent fewer breast cancer deaths compared to women of the same age who weren't screened. While that number sounds impressive, it isn't when put in context, Berry said. After accounting for different numbers of total women in the two arms of the trials, the difference in mortality between the groups represents the18 percent reduction in death.
Some women die from breast cancer even if their cancers are small when detected by mammography.
The difficulty with mammography is that no one can say for sure what the cancer that is detected will do, said Berry. All women can do is to think carefully about the question and decide what is appropriate for themselves.