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 The research, published on Wednesday in the British
Medical Journal, is the latest salvo in a decades-long debate over
the benefit of mammograms. The 25-year study of 89,835 women in
Canada, aged 40 to 59, randomly assigned the volunteers to receive
either annual mammograms plus physical breast exams or physical
exams alone.
The women started receiving mammograms from 1980 to 1985. At the
time, doctors believed screening saved lives by detecting
early-stage cancers, which were considered more treatable than
cancers detected later, especially in women aged 50 to 64.
Instead, the study "found no reduction in breast cancer mortality
from mammography screening," the scientists wrote, "neither in women
aged 40-49 at study entry nor in women aged 50-59."
The findings echo research such as a 2012 study in The New England
Journal of Medicine which found that screening mammography "is
having, at best, only a small effect on the rate of death from
breast cancer." On the basis of similar findings going back to the
1990s, the U.S. Preventive Services Task Force, an independent panel
of medical experts, in 2009 recommended biennial screening
mammography for women 50 to 74 years, replacing an earlier
recommendation that women start having mammograms every one to two
years at age 40.
Proponents of mammograms often point out that women whose breast
cancer is diagnosed by mammography alone live longer than those
whose cancer is diagnosed by physical exam. This study found that as
well, but the apparent advantage was illusory, the researchers
concluded. For one thing, if a cancer is sufficiently aggressive and
resistant to treatment it will likely prove fatal no matter when it
is detected. Finding it in 2011 by physical exam, as opposed to 2007
by mammogram, simply means that the woman lives longer knowing that
she has cancer, not that she lives longer overall.
Mammograms, the study found, increase perceived survival time
without affecting the course of the disease.
In addition to not reducing mortality from breast cancer, the study
found, mammograms are leading to an epidemic of what the researchers
call "over-diagnosis." Nearly 22 percent of the invasive cancers
detected by mammography were harmless, meaning they would not cause
symptoms or death during a woman's lifetime.
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This represents one over-diagnosed breast cancer for every 424
women who received mammography screening, calculate the researchers,
who were led by epidemiologist Anthony Miller of the University of
Toronto.
He and his colleagues stressed that the results may not hold in
countries where access to advanced cancer treatment is limited.
But in countries such as those in North America and Europe where it
is, the scientists wrote, "our results support the views of some
commentators that the rationale for screening by mammography should
be urgently reassessed by policy makers," since annual mammography
"does not result in a reduction in breast cancer specific mortality
for women aged 40-59 beyond that of physical examination alone or
usual care."
An accompanying editorial agrees that policy makers should stop
pushing mammograms but points out that this is easier said than
done: "governments, research funders, scientists, and medical
practitioners may have vested interests in continuing" that push,
since mammography is a multibillion-dollar industry. Annual
screenings also give women the sense that they are taking active
steps to reduce the chance of dying of breast cancer.
In a statement, the American College of Radiology and Society of
Breast Imaging called the BMJ study "an incredibly misleading
analysis." The results "should not be used to create breast cancer
screening policy as this would place a great many women at increased
risk of dying unnecessarily from breast cancer."
(Reporting by Sharon Begley; editing by
David Gregorio)
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