A new study suggests "false alarms" in breast cancer screenings might not be so benign after all.
A Danish study of more than 58,000 women found those who had false positive mammograms, meaning the results suggested breast cancer when there was none, had a 67 percent higher risk of developing breast cancer later in life compared with women who had negative mammograms.
"The excess breast cancer risk in women with false-positive tests may be attributable to misclassification of malignancies already present at the baseline assessment ... or to a biological susceptibility for developing breast cancer in some women without malignancies at baseline," the study authors wrote, describing how dense, irregular breast tissue may disguise or develop into cancer.
The study was published today in the Journal of the National Cancer Institute.
The U.S. Preventive Services Task Force recommends biennial mammograms for women between the ages of 50 and 74. The test, an x-ray of the breast, can detect breast cancer early and increase the odds of survival. But it can also lead to false positives, prompting unnecessary tests and procedures, not to mention anxiety.
"Any abnormal finding sends a woman into a tailspin," said Lillian Shockney, a breast cancer nurse at Johns Hopkins Hospital in Baltimore. "It's awful. But she would rather know if she has something ominous in her breast or not."
It's estimated that for one woman's life to be saved through mammography, 2,000 women have to be screened and 200 will get a false positive. False positives usually lead to biopsies, which remove a tiny piece of the questionable tissue for further tests. But 10 of 200 women with false positives will undergo unnecessary surgery.
The link between false positives and breast cancer is unclear. But Dr. Susan Love, president of the Dr. Susan Love Research Foundation, said women who have a family history of breast cancer are more likely to have a false positive.
"It so subjective," she said of a radiologist's decision to follow up a suspicious mammogram with a biopsy. "If you had a mother with breast cancer, the radiologist and ... probably you yourself would be more aggressive in following up any slightly suspicious abnormality in a screening mammogram."
But there are other, more biological explanations, too.
"Surgery or needle biopsies may cause a local inflammatory or wound-healing reaction, which increases cancer risk," or "the extra radiation from the workup for the false positive could increase breast cancer," said Love. "Or we might be picking up on some subtle change in the microenvironment, the fibrous tissue, that's more conducive to cancer growing. We just don't know."
The study included women between the ages of 50 and 69 in Denmark, a country with a universal health care system.
Dr. Marisa Weiss, president of BreastCancer.org, said American doctors would almost always follow up on suspicious mammogram results out of fear of litigation.
"The biopsy rate is higher here than in places like Denmark," she said. "We have no tolerance for uncertainty or missed diagnoses."
But with advances in diagnostic technology, the false positive rate is falling. A study published Tuesday in the Journal of the American Medical Association found using ultrasound and MRI in addition to mammography boosted breast cancer detection in high-risk women.
"Mammography is just one tool in the shed," said Weiss. "One thing this study shows is that additional diagnostic tools need to be used in a careful way to help identify those women who would benefit from a biopsy. We need to give women the benefit of early detection while avoiding both false positives and false negatives."
Weiss said the Danish study also highlighted the importance of routine checkups after a false positive.
"Women who had a false positive still need to be followed carefully over time," she said. "Even though the last thing you want to do is go back for another mammogram."