April 5, 2012 -- More than half of women in the U.S. who get annual mammograms will have at least one false-positive reading after 10 years of screening, and now new research suggests that these women may be at increased risk for breast cancer.
Women in a Danish study who had at least one false-positive mammogram were more likely to eventually be diagnosed with breast cancer than women with no such history.
But there was little difference in risk among women with and without false-positive readings who were screened after the year 2000, suggesting that advances in mammography screening technology have led to more accurate testing.
"This study could be interpreted as reassuring for women being screened today," says breast cancer specialist Stephanie Bernik, MD, who was not involved with the study.
Bernik, who is chief of surgical oncology at Lenox Hill Hospital in New York City, says innovations in mammography screening since 2000 have led to better detection of breast cancer and fewer false-positives.
"There has long been a suggestion that women who have more activity in their breasts that lead to false-positive mammograms may also have an increased risk for breast cancer, but I don't think this study proves this," she tells WebMD.
False-Positive Test, More Breast Cancer
Women with positive mammography screenings -- whether false or not false -- typically have additional mammograms or ultrasound, followed by a biopsy to confirm or rule out breast cancer if the results are still unclear.
False-positive mammography readings are especially common in women with breasts that are dense or have other characteristics including benign growths that look like tumors, calcium deposits, skin thickening, newly retracted nipples, or suspicious lymph nodes.
Several previous studies have suggested that women with these breast characteristics have an increased risk for breast cancer, but the research is inconclusive.
In the newly published study, researchers from the University of Copenhagen examined data from a population-based mammography screening program in Denmark.
The analysis included 58,000 women who had mammograms in that country between 1991 and 2005.
A false-positive mammogram was associated with a 67% greater likelihood of eventually receiving a diagnosis of breast cancer.
Women Screened Later Had Lower Risk
But the increase in risk among women who had mammograms after the year 2000 was roughly half that of women screened in the mid-1990s, and it was not considered significant.
University of Copenhagen associate professor of epidemiology and researcher My von Euler-Chelpin, PhD, says this suggests that screenings before 2000 may have missed more existing cancers.
The study appears in the May issue of the Journal of the National Cancer Institute.
"After 2000 the breast cancer detection rate increased and false-positives decreased," she tells WebMD. "But the fact that the increase in risk remained for many years after screening also suggests that the breast characteristics that lead to false-positives may be associated with increased [breast cancer] risk."
She adds that more study is needed to confirm the association.
U.S. May Be Different, Expert Says
Even if the results are confirmed, it is not clear if the findings apply to women in the United States, Bernick says.
That is because far more women in the U.S. are called back for second-look screenings or biopsies after initial mammograms.
"We have a much lower threshold for calling women back because of the nature of our health care system, so you can't necessarily equate what is happening overseas to what is happening here," Bernick says.
A nationwide study published last October found that 61% of women in the U.S. screened annually for 10 years will have at least one false-positive reading, and up to 1 in 10 with false-positive results will have received a recommendation for a biopsy.
Bernick says some women who have had false-positive mammograms or benign biopsies in the past may be less concerned than they should be about future findings.
"A woman should never ignore a new finding based on a history of false-positive mammograms," she says.