TUESDAY, Feb. 11, 2014 (HealthDay News) -- The value of yearly
mammograms is under fire once again, with a long-running Canadian
study contending that annual screening in women aged 40 to 59 does
not lower breast cancer death rates.
For 25 years, the researchers followed nearly 90,000 women who
were randomly assigned either to get screening mammograms or
"Mammography detected many more invasive breast cancers," said lead researcher Dr. Cornelia Baines, professor emeriti at the University of Toronto's Dalla Lana School of Public Health. "Survival time was longer in women getting mammography."
"[However], the number of deaths from breast cancer was the same in both groups at 25 years," she said.
"It is increasingly being recognized that there are significant harms from screening, and that screening can do much less now than 40 years ago because of improved therapy," Baines added. "Twenty-two percent of the mammography group with screen-detected invasive beast cancer were over-diagnosed and unnecessarily inflicted with therapy."
Over-diagnosis is defined as the detection of harmless cancers
that will not cause symptoms or problems during a patient's
The study, which began in 1980 in 15 screening centers in six
Canadian provinces, was published Feb. 11 in the online edition of
Women in the mammography group had a total of five mammograms --
one a year for five years. Those aged 40 to 49 in the mammography
group and all women aged 50 to 59 in both groups also had an annual
physical exam. Women aged 40 to 49 in the no-mammography group had
a single physical exam followed by typical care.
During the next 25 years, 3,250 women who got screening
mammographies were diagnosed with breast cancer, compared with
3,133 in the no-mammography group, according to the study. While
500 women in the mammography group died during the follow up, 505
in the no-mammography group did.
In 2009, the U.S. Preventive Services Task Force updated its
recommendations on screening mammograms, suggesting them for women
aged 50 to 74 every two years. Among women aged 40 to 49, the task
force recommended only a discussion with a woman's doctor on the
pros and cons of screening.
But other U.S.-based organizations, including the American
Cancer Society, continue to recommend annual screening mammograms
for women beginning at age 40.
The American College of Radiology, which also supports annual
screening mammograms for women aged 40 and older, reacted strongly
to the Canadian findings. In a statement issued Feb. 11, the
college called the report "an incredibly misleading analysis based
on the deeply flawed and widely discredited Canadian National
Breast Screening Study."
Among those flaws, according to the college: the quality of
mammograms done in the study was poor and the skills of the imaging
technologists were not adequate.
The new report isn't a surprise, said Dr. Carol Lee, chairwoman
of the college's breast imaging communications committee. "When it
was first reported 20 years ago, it didn't show a benefit," she
The findings are at odds with many other reports that show a
benefit for routine screening, Lee added.
"Screening mammography has been shown over and over again to decrease mortality from breast cancer," she said.
Lee said she is "concerned [the new study] is going to
discourage women from having mammograms."
In an editorial accompanying the study, experts from the
University of Oslo, the Harvard School of Public Health and other
institutions agreed with the Canadian researchers that the
rationale for screening needs to be reassessed by policy
Baines said her research points to the value of offering
screening mammograms only to those at higher risk of breast
"In time, the hope is to offer screening to a subset of the population [that has] been identified, probably by genetic markers, to be very likely to benefit from screening," she said.
To learn more about mammography, visit the
American Cancer Society.
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