Eileen Moleski has received mammogram results suggesting she has breast cancer four times, but further testing showed, each time, that she didn't have the disease.
Now, she gets anxious each time she's due for another mammogram, said Moleski, 44, who lives in the Philadelphia area.
The findings suggest "that either that the false positive mammograms may not be false at all, or that the false positive mammograms may be representative of a biological process which contributes to elevated risk of developing breast cancer in the future," said Dr. Richard Bleicher, of the Fox Chase Cancer Center, in Philadelphia.
The study is published today (April 5) in the Journal of the National Cancer Institute.
A heightened risk
Researchers at the University of Copenhagen compiled mammography data from more than 58,000 Danish women. The women in the study were between 50 and 69 years old, and were screened between 1991 and 2005.
The findings showed that 339 cases of breast cancer would be expected in one year in a group of 100,000 women who had only negative mammograms , whereas 583 cases would be expected in a year in a group of 100,000 women who'd previously had a false-positive mammogram.
The increased risk of breast cancer remained for six years after a false positive mammogram, compared with women who always had a negative mammogram.
The findings showed an association, not a cause-and-effect link, and further work is needed to confirm the results.
Still, similar findings have been shown in the United States, said Dr. Jeff Tice, of the Helen Diller Family Comprehensive Cancer Center in San Francisco, who was not involved in the study.
The link might be explained by breast density , Tice said. Women with higher-density breast tissue may be more likely to get a false positive mammogram, and studies, including one that Tice worked on, have shown these women also have increased risk of developing breast cancer.
Dr. Dana Whaley, an assistant professor of radiology at the Mayo Clinic in Rochester, Minn., agreed that breast density may be the common link.
"Breast density is an independent risk factor for breast cancer, and it is more significant than family history most of the time," Whaley said, though he added that why this is the case is not understood.
The study researchers said that the new findings suggest that false positives are a sign of some change occurring in breast tissue. It's not likely, they said, that there actually was a tumor that was missed in follow-up evaluation: women in the study with a false-positive mammogram tended not to develop cancer within two years of their false-positive tests.
Skepticism of a link
Some experts raised cautions about the new findings.
"We don't know other critical factors about the risk of the patients in the study — family history, genetic mutations, hormone use," Bleicher said. The false-positive test might not, in itself, be the risk factor for cancer— it may be related to something else entirely.
The findings would be more convincing if the study researchers had linked the specific location within the breast of the abnormality that caused the false positive with the location of later breast cancer, said Dr. Karla Kerlikowske, also of the Diller Cancer Center.
The underlying biology that might increase the risk of breast cancer in these women needs to be explained with follow-up studies, Kerlikowske said.
Like Moleski, many patients with previous false-positive mammograms have anxiety, Whaley said. But that anxiety is usually about the detection of cancer, not the false-positive result. "When and how this information is presented to women is very important in preventing unnecessary anxiety,"hesaid.