Importance of Mammograms
However, review didn't include women in their 40s, so debate may not end
Before this standardized review, the number of women who must be screened to prevent one death ranged from 111 to 2,000 among the studies. Smith's team found that estimates of the benefits and harms were all based on different situations.
Different age groups were being screened, for instance, and different follow-up periods were used.
Some studies looked at the number of women for whom screening is offered and others looked at the number who actually got mammograms. There often is a huge difference between those two groups, Smith said.
"Thirty to 40 percent don't show up, and they are counted as having a mammogram [although they did not] when they die of breast cancer," he said. "This hugely depresses the benefits."
"If you don't have a long follow-up, you are not able to accurately measure the benefit," Smith said. "Some women die 20 or more years after the diagnosis."
After the researchers used a single, common scenario, the gap in benefit estimates among studies dropped substantially -- ranging from 64 to 257 women who must be screened to prevent a single death from breast cancer.
Dr. Michael LeFevre, co-vice chairman of the USPSTF, reviewed the new findings but was not involved in the study. "For women aged 50 to 69, it confirms that mammography can reduce deaths from breast cancer," he said.
The new analysis, LeFevre said, doesn't include women in their 40s, which is one of the central parts of the ongoing debate about the use of screening mammography.
The task force is in the process of updating the 2009 recommendation, said LeFevre, who is also a professor of family and community medicine at the University of Missouri. "[The update] is not in response to the re-analysis," he said. "It's standard timing for an update."