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 Diagnosis rates for early-stage tumors and pre-invasive malignancies
known as ductal carcinoma in situ (DCIS) have surged in recent years
as more women get screening mammograms.
The current study offers fresh evidence linking routine screening to
over-diagnosis of non-aggressive tumors because it compares outcomes
over a single time period in two regions of Denmark – one that
offered biennial mammography for women aged 50 to 69 and one that
didn’t.
“Overdiagnosis means that healthy women get unnecessary breast
cancer diagnoses,” said lead study author Dr. Karsten Juhl
Jorgensen, of the Nordic Cochrane Center and Rigshospitalet in
Copenhagen.
“A breast cancer diagnosis is a life-changing event for the woman
and her family, with substantial implications for their quality of
life,” Jorgensen added by email. “It also leads to overtreatment
with surgery, radiotherapy and sometimes chemotherapy – we know
these treatments have serious, sometimes lethal, consequences.”
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 attack.
To see how well mammograms achieve this ideal, researchers examined
data on more than 1.4 million Danish women aged 35 to 84 from 1980
to 2010.
Organized breast cancer screening programs began in Copenhagen in
1991, Funen in 1993 and Frederiksberg in 1994 – altogether covering
about 20 percent of the population. Other regions gradually
introduced screening starting in 2007.
Screening wasn’t associated with a lower incidence of advanced
tumors, researchers report in the Annals of Internal Medicine.
This raises doubts about whether mammography reduces breast cancer
deaths, the researchers conclude.
In addition, researchers estimate that as many as one in three
breast tumors diagnosed in women who got mammograms would never have
caused a noticeable health problem or led to death – and are
therefore examples of overdiagnosis.
One limitation of the study is that because mammography has improved
since this study began in 1980, women might get different results
today, the authors note.
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While the study adds compelling evidence that routine mammograms
carry a risk of overdiagnosis, that doesn’t mean it’s time for
screening guidelines to change, Dr. Otis Brawley, chief medical
officer of the American Cancer Society, said in a phone interview.
Under current U.S. guidelines, mammograms should be optional for
women aged 40 to 44, then done annually from 45 to 54. Women 55 and
older should switch to mammograms every two years, continuing as
long as they are in good health with a life expectancy of at least a
decade.
“This isn't about saying don't get a mammogram, this is about using
it most effectively to save the most lives,” said Brawley, who wrote
an editorial accompanying the study.
Beyond screening, there are other preventive measures women
shouldn’t overlook like eating well, getting plenty of exercise, and
maintaining a healthy weight.
In the future, it may be possible to use screening results to
pinpoint women who might be candidates for “watchful waiting,” the
close follow-up without treatment that’s common for many men with
early-stage prostate cancer, Brawley said.
“We aren't ready for that because we don't know what watchful
waiting looks like for breast cancer yet,” Brawley said.
So for now, that means accepting that overdiagnosis and screening go
hand in hand, along with the potential for some women to get
unnecessary treatment.
“If it's small and slow-growing, I think all breast cancers ought to
be treated,” Brawley added.
SOURCE: http://bit.ly/2jw79ua Annals of Internal Medicine, online
January 9, 2017.
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