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 The new guidelines released today by the Canadian Task Force on
Preventive Health Care are similar to recommendations released in
2011, researchers note in CMAJ. But the updated recommendations may
encourage more women, particularly those under 50, to opt against
screening mammograms, said vice-chair of the task force Dr. Ainsley
Moore.
"The evidence continues to show a close balance between potential
benefits and harms of breast cancer screening," Moore said by email.
"This balance appears to be less favorable for younger women."
The goal of mammograms is to detect tumors before they can be felt
in a physical breast exam, catching cancer sooner when it's easier
to treat. Ideally, this should mean fewer women are diagnosed when
tumors are bigger, rapidly growing, and harder to control.
But a growing body of evidence suggests that widespread breast
cancer screening may catch more small, slow-growing tumors that are
unlikely to be fatal, without curbing the number of cancers that are
diagnosed at a late stage. And catching more small, slow-growing
tumors may needlessly expose women to invasive follow-up testing and
treatments.
For the current recommendations, researchers examined the latest
evidence on the outcomes from screening mammograms, which are done
for women without symptoms and do not include patients who feel a
lump in their breast. Among other things, researchers examined 29
studies assessing the value women place on the anticipated benefits
and harms from screening.
The task force recommends against screening women aged 40 to 49
years but encourages women in this age range who prefer to be
screened to discuss this with their doctor. Women in this age group
face a higher risk of potential harms from false positives,
overdiagnosis and overtreatment compared with other age groups, and
the absolute benefit is smaller, researchers note.
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From age 50 to 74, women should get a screening mammogram every two
to three years, the task force recommends. This is also dependent on
women's own values and preferences, and women may choose not to be
screened if they are concerned about overdiagnosis.
While the task force recommends mammograms, it advises against
screening with magnetic resonance imaging, tomosynthesis and
ultrasonography in women not at high risk for breast cancer.
"The studies of mammography are reassuring in that they suggest that
women who start screening after age 50 do not lose much in terms of
breast cancer outcomes - that's why many guidelines don't recommend
beginning until later," said Dr. Deborah Korenstein of Memorial
Sloan Kettering Cancer Center and Weill Cornell Medical College in
New York City, who wrote an editorial published with the study.
"It's clear that starting screening later prevents unnecessary tests
and treatments," Korenstein said by email.
However, screening younger women does save some lives. When women
get screened in their 40s, this saves one life for every 1,700
people screened, Korenstein said.
"For some women that small benefit might lead them to want screening
despite the potential downsides, which highlights the important of
taking personal preferences into account," Korenstein added.
SOURCE: http://bit.ly/2B6ZJ71 CMAJ, online December 10, 2018.
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