Mammography is considered the best screening tool for finding breast cancer early, when it is most treatable. But it's far from perfect. A new study this week provides more proof of what many women have learned the hard way: A lot of mammograms raise false alarms.
In fact, a full 80 percent of the women who get that frightening summons for another mammogram after the first seemed to reveal something suspicious turn out not to have cancer.
The study, conducted by the national Breast Cancer Surveillance Consortium and published this week in the Annals of Internal Medicine, looked at how often women are likely to be called back for additional testing after a decade of annual screening mammography. Researchers found that more than half of women who don't have cancer will be recalled at least once in 10 years of mammography; about one in 12 will be referred for a biopsy.
False positives are upsetting, but they also can lead to unnecessary and costly medical procedures. And the experience can turn some women off from getting mammograms in the future.
The good news: There are steps women can take to cut their risk of a false positive mammogram by as much as half.
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Why do radiologists, the medical specialists who read mammograms, get it wrong so often?
Though the images you see here, of a California woman's breast taken 12 months apart, clearly show cancer developing, reading mammograms can be extremely difficult, even with newer digital technology. The clearest images tend to be made in older women, whose breasts are fattier. But younger women's breasts are denser, with normal but fibrous tissue that looks white on mammograms (which are in black and white) and can conceal a small cancer.
"We are looking for small things, really, really small things that resemble cancer. They're hard to spot," said Dr. Chris Flowers, a Moffitt Cancer Center breast cancer specialist and one of the study co-authors.
That's one reason Flowers wants women to get annual mammograms, so that small changes are found more quickly. The study did find that women who get screened only every other year — as some experts including the U.S. Preventive Services Task Force recommend — are less likely to have false positives. But that could be just because they have fewer mammograms, Flowers noted.
Radiologists are guided in what to look for by national standards and recommendations. "But it's not all black and white," said Dr. Barbara Bourland, medical director of the Morton Plant Mease Susan Cheek Needler Breast Centers.
Gather a group of breast cancer radiologists and they will each likely have different opinions about what features in a mammogram warrant a recall. Set the bar too high, and you risk missing early stage cancers. Set the bar too low, and you re-test too many women.
"Good (radiology) practices watch their recall rate," said Bourland, "If you're recalling more than 10 percent of patients, you're probably bringing back way too many for retesting. But if you're only recalling one percent, you're probably missing a lot of cancer."
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That's why her top tip for women is to insist on knowing the expertise of the radiologist reading their films.
"The radiologist should be reading mammograms daily. Under 2,000 a year is very low," said Bourland, who estimates she reads about 20,000 mammograms a year.
How can you know? When you call to make your appointment, ask who the radiologist is, and how many films he or she has read in the past year. If they can't tell you, go somewhere else.
Bourland also said women who are recalled should insist that the same physician who read the screening mammogram also handles subsequent diagnostic work ups.
Flowers says women should either go to the same imaging center every year, or get their previous mammograms and bring them to the new center.
"Having prior films for comparison cuts your chances of being recalled in half," said Flowers, "We're looking for small changes. If there's something new from one year to the next, you're going to see that change."
Request a CD of your mammograms if you are moving or changing screening centers. While it's good to provide your last two years of mammograms, having the last five years is even better, said Bourland.
Irene Maher can be reached at firstname.lastname@example.org