Women who have an abnormal mammogram should stay vigilant for cancer for for the next decade, even when follow-up tests fail to detect cancer, a study released Wednesday finds.
That's because there's a "modest" risk that cancer will develop during the next decade, says lead author Louise M. Henderson of the University of North Carolina School of Medicine in Chapel Hill.
The absolute increase in risk amounts to about 1 additional cancer in every 100 women who have a false positive mammogram over a 10-year period, she says.
But when put another way, the numbers may appear alarming. The study divided women into two groups — those who got additional imaging and those who also got biopsies.
Women with an abnormal screening mammogram had a 39 percent higher risk of cancer if they got additional imaging that turned out to be negative, too. That's compared with women who were truly negative and never developed breast cancer.
For women who got biopsies that turned out negative, the chance of cancer was increased by 76 percent over the next 10 years.
"We don't want women to read this and feel worried," Henderson says. Instead, the findings should be considered one more "useful tool" when weighing all the other factors that might be raising a particular woman's risk, such as age, race, breast density and family history of breast cancer.
Henderson says the study wasn't designed to figure out why a falsely positive mammogram is associated with an increased cancer risk.
It's possible, she says, that the increased risk "could be the fact that the radiologist sees an abnormal pattern that's not cancerous, but it's a radiographic marker," and it could be that this is a precursor to some subsequent cancer diagnosis.
The study, done at several leading universities, looked back at more than 2.2 million screening mammograms considered to be false alarms between 1994 and 2009. It was published Wednesday in Cancer Epidemiology, Biomarkers & Prevention. The mammograms were done in 1.3 million women, ages 40 to 74.
Earlier studies have had conflicting results. But the size of this study makes researchers more confident that whatever is going on is a true phenomenon and not chance, says Dr. Richard Wender, chief cancer control officer of the American Cancer Society.
"If you've had a false positive, that is a risk factor," he says, "so it's very important that a woman stay up to date with regular mammography."
As it is now, Wender says, at least one-third of women who should be getting routinely screened for breast cancer are falling behind schedule.
The cancer society created controversy in October, when it changed its guidelines to recommend that regular screening start at age 45. Other groups recommend starting earlier, at age 40, and some say it's OK to wait until age 50.
Studies have shown that the chance of getting an abnormal screening mammogram that is falsely positive is about 50 percent over the course of 10 years. That often leads to further testing, including more mammograms, possible ultrasound exams, MRIs and even biopsies.
STEVE INSKEEP, HOST:
This story gives people even more to think about when they think about mammograms. Sometimes a mammogram gives the wrong test result and the wrong result eventually turns out to be right. I'm just going to say that again. You take a test, it falsely shows signs of cancer, yet people who had false results are slightly more likely to develop cancer later. That's according to a new study in a journal of the American Association for Cancer Research. Here's NPR's Patti Neighmond.
PATTI NEIGHMOND, BYLINE: Mammograms are important tools for detecting breast cancer. But they can also cause unnecessary distress, turning up false alarms, what doctors call false positives. Epidemiologist Louise Henderson with the University of North Carolina School of Medicine.
LOUISE HENDERSON: Over the course of, say, 10 years of annual screening or biannual screening, it's estimated that about 50 percent of women will experience a false positive finding.
NEIGHMOND: And that typically leads to further testing, more mammograms, maybe ultrasounds, MRIs, even biopsies. And a false positive is what it sounds like. It's a positive finding for cancer but it's false. Henderson's also a breast cancer screening researcher, and she wanted to see what happened to women down the road up to 10 years after having a false positive mammogram. She analyzed medical records for 1.3 million women across the country.
HENDERSON: We found that women who had a false positive mammogram had an increased risk of subsequently developing breast cancer compared to women who did not have a false positive finding.
NEIGHMOND: Now Henderson says it's important to note the increase was small - about one additional case of cancer out of every 100 women who had a false positive mammograms. But it is an increase in cancer risk nonetheless, she says. Her study was not able to explore why this may be the case.
HENDERSON: The increased risk could be the fact that the radiologist sees an abnormal pattern that's not cancerous but it's a radiographic marker. And it could be that that is a precursor to some subsequent cancer diagnosis.
NEIGHMOND: Henderson says the findings should help doctors determine overall cancer risk for their patients, along with other known risk factors, like age, breast density and family history. This is not the first study to look into false positive mammograms and breast cancer risk. But it's the largest, says Dr. Richard Wender, chief cancer control officer at the American Cancer Society.
RICHARD WENDER: The most important message here is that if you've had a false positive, that is a risk factor - a small one but a real one - to be at higher risk for a breast cancer diagnosis in the future. So it's very important that a woman stay up to date with regular mammography.
NEIGHMOND: The American Cancer Society recently revised its recommendations for breast cancer screening, and now says women don't need to start getting yearly mammograms until they turn 45. Other groups recommend other start dates. Even so, Wender says the conversation should begin at age 40 with a woman and her doctor evaluating all risk factors and deciding whether to start mammography earlier.
WENDER: But if you've had a false positive, it's even more important that a woman remain vigilant and their clinician and the entire health care system help her remain vigilant to be regularly screened.
NEIGHMOND: As it is now, Wender says at least one-third of women who should be getting routinely screened for breast cancer are falling behind in their recommended mammogram schedule. Patti Neighmond, NPR News. Transcript provided by NPR, Copyright NPR.