Researchers caution that women should not be afraid and skip mammograms, as the actual risk to any given woman is still low.
The study involved nearly 60,000 women participating in the Copenhagen mammography program. As part of the program, all women aged 50 to 69 in the city get an invitation to come in for a mammogram every two years.
Results showed that women who had false positives were 73% more likely to develop breast cancer in the two years before their next mammogram and 33% more likely to develop breast cancer over the next 17 years, compared with women who didn't have false positives.
Still, only 22 of the 5,080 women who had false-positive results developed breast cancer in the next two years, says researcher My von Eular-Helpin, PhD, an assistant professor of public health at the University of Copenhagen.
Women who have false positives may want to make sure they are monitored more closely, perhaps with more frequent mammograms, she says.
Some Breast Lesions May Be Missed
Although the study didn't look at why these women were at increased risk of breast tumors, Eular-Helpin tells WebMD she suspect that some benign lesions turned malignant. Also, some lesions are so small they may be missed, especially by a less experienced radiologist, she theorizes.
Claudia Isaacs, MD, director of the clinical breast cancer program at Georgetown Lombardi Comprehensive Cancer Center, says the findings offer one more reason to for women 50 and older to have annual breast X-rays.
There's been a debate in the U.S. ever since the U.S. Preventive Services Task Force, an independent panel of experts, said women 50 and older need mammograms only every two years. The American Cancer Society and some other cancer groups have long recommended that women get annual mammograms starting at age 40.
Just yesterday, researchers reported that half of insured women in the U.S. don't get regular mammograms.
"If you have a false-positive result, don't get scared. Just follow up with yearly mammograms," Isaacs tells WebMD.
The findings were presented at the San Antonio Breast Cancer Symposium.
This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.