WEDNESDAY, Dec. 11, 2013 (HealthDay News) -- Often-conflicting
results from studies on the value of routine mammography have only
fueled the debate about how often women should get a mammogram and
at what age they should start.
In a new analysis of previous research, experts have applied the
same statistical yardstick to four large studies and re-examined
the results. They found that the benefits are more consistent
across the large studies than previously thought. All the studies
showed a substantial reduction in breast cancer deaths with
"Women should be reassured that [mammography] is quite effective," said study researcher Robert Smith, senior director of cancer screening for the American Cancer Society. Smith is scheduled to present the findings this week at the 2013 San Antonio Breast Cancer Symposium.
The findings also were published in the November issue of the
Breast Cancer Management.
In 2009, the U.S. Preventive Services Task Force (USPSTF), an
independent group of national experts, updated its recommendation
on mammography, advising women aged 50 to 74 to get mammograms
every two years, not annually. The group also advised women aged 40
to 49 to talk to their doctors about benefits and harms, and decide
on an individual basis whether to start screening. Other
organizations, including the American Cancer Society, continue to
recommend annual screening mammograms beginning at age 40.
In assessing mammography's benefits and harms, researchers often
look at the number of women who must be screened to prevent one
death from breast cancer -- a number that has ranged widely among
In assessing harms, experts take into account the possibility of
false positives. Other possible harms include finding a cancer that
would not otherwise have been found on screening (and not been
problematic in a woman's lifetime) and anxiety associated with
Smith's team looked at four large, well-known reviews of the
benefit of mammography. These included the Nordic Cochrane review,
the U.K. Independent Breast Screening Review, the USPSTF review and
the European Screening Network review.
To standardize the estimates of how many women need to be
screened to prevent one breast cancer death, the researchers
applied the data from each of the four reviews to the scenario used
in the U.K. study.
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."
To learn more about the task force's recommendations for
screenings, visit the
U.S. Preventive Services Task Force.
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