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 An increased risk of breast cancer among women with a “false
positive” mammogram has been reported before. What’s new about this
study is that the authors tried to figure out how much, if any, of
the extra risk is simply due to doctors missing the cancer the first
time they investigated the worrisome mammogram findings.
But mistakes from doctors missing cancers explained only a small
percentage of the increased risk, according to lead author My von
Euler-Chelpin, an epidemiologist from the University of Copenhagen
in Denmark.
She told Reuters Health in a telephone interview that she could not
explain most of the increased risk of later breast cancer in women
with false-positive mammograms. (A mammogram is considered false
positive when it suggests possible breast cancer but additional
screenings or a biopsy fails to find it.)
Of more than 58,000 Danish women who had mammography between 1991
and 2005, her study identified 4,743 women with suspicious findings
that were eventually declared negative.
By 2008, 295 of those 4,743 women had been diagnosed with breast
cancer, von Euler-Chelpin and colleagues reported in Cancer
Epidemiology.
Radiologists reread the original mammograms and found that doctors
had actually missed the cancer in 72 of the 295 women, for a
false-negative rate of 1.5 percent. Even after taking those missed
cancers into account, however, the researchers found that women with
false-positive mammograms were still 27 percent more likely to be
diagnosed with breast cancer years later, compared to women with
only negative test results.
The risk was slightly higher in women who had surgical biopsies that
turned out to be negative.
Von Euler-Chelpin thinks a smaller percentage of American women
would have an elevated risk for breast cancer after a false-positive
test because the U.S. has a higher rate of false positives than
Denmark. The risk of a false-positive test over 10 mammograms ranges
from 58 percent to 77 percent in the U.S., while it is around 16
percent in Denmark, the study says.
Dr. Michael Alvarado, a breast cancer surgeon from the University of
California, San Francisco, agreed that the risk of being diagnosed
with breast cancer after a false positive mammogram is probably
lower in the U.S. than in Denmark.
“It’s hard to translate the data to the U.S. population because we
have such a different screening program, we tend to biopsy
everything, and we’re much more aggressive,” he told Reuters Health.
Alvarado was not involved in the current study.
“Is there some inherent biology of the breast that makes it
suspicious and it puts you at higher risk? I don’t think anyone
knows what it is,” he said.
Alvarado wondered if women who get false-positive mammograms should
be followed more closely by their doctors, or if false-positive
patients should be screened differently.
Von Euler-Chelpin told Reuters Health the excess rate of breast
cancer among women who have had false-positive mammograms points to
the need to personalize screening programs for women - and Dr. Karla
Kerlikowske agreed.
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Kerlikowske, from the University of California, San Francisco, is
developing a risk calculator app to guide women in deciding how
often to get mammograms. The calculator considers a range of
factors, including age, race, previous breast cancer, family history
and breast density. Kerlikowske was not involved in the current
study.
Although having had a false-positive mammogram is associated with a
woman’s breast cancer risk, Kerlikowske points out that the actual
risk of being diagnosed with breast cancer remains low.
The average five-year breast cancer risk for a 50-year-old white
woman with no prior family history of breast cancer is 1.25 percent,
the calculator shows. It ranges from less than 1 percent, to 2.70
percent, depending upon breast density, for the same woman with a
history of a prior breast biopsy, regardless of whether the biopsy
was positive or negative.
“The absolute risk is still small,” Kerlikowske said. “To me, it
just says, now you have this risk factor, and you have to consider
it with other risk factors.”
Von Euler-Chelpin agrees.
“This paper is one little step on the way of trying to identify
high-risk groups,” she said. “The goal is to find more personalized
screening programs for women.”
The American Cancer Society recommends that women be screened for
breast cancer every year they are in good health starting at age 40.
But a growing number of researchers have questioned the benefits of
annual mammograms, and since 2009 the government-backed United
States Preventive Services Task Force has recommended that screening
be done every two years and be generally restricted to women aged 50
to 74.
Women in Denmark between the ages 50 to 69 are invited to have
screening mammograms every other year, Von Euler-Chelpin said.
Getting a mammogram every other year instead of annually did not
increase the risk of advanced breast cancer in women ages 50 to 74,
according to a study Kerlikowske published last year. (see Reuters
story of March 18, 2013 here: http://reut.rs/1w7CMuh)
The recommendation to reduce the frequency and delay the start of
mammography screening was based on research showing the risk of
false-positive results – which needlessly expose women to the
anguish of a possible breast cancer diagnosis and the ordeal of
further testing – outweighed the benefits of detecting cancers
earlier.
SOURCE: http://bit.ly/1wALk81 Cancer Epidemiology, online July 14,
2014.
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