False positives may provide clue to future breast cancer risk

A large new study out today finds women who had a false positive mammogram had an increased risk for developing breast cancer years later. The risk was independent of breast density and remained elevated for a decade after the false-positive test. The study appears in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.

Some other studies had previously shown false positives were associated with a higher risk of cancer, but not consistently. So this study’s size, with over 1.3 million women who underwent more than 2 million exams, makes it notable. It confirms that certain irregular findings in mammograms that are found not to be cancer appear to be associated with an increased risk of being diagnosed with breast cancer later.

But the most important number to keep in mind may be what this increased means in real life. While having a false alarm was associated with a relative increase of 40% (for those who underwent additional imaging) to 75% (for those who underwent a biopsy), the absolute risk over a 5 or 10 year period was not large. After five years, about 2% of women who had a false positive were diagnosed with cancer, compared to about 1% of women who had negative mammograms.

Still, there is some increased risk over the short term, and for up to 10 years of follow-up. Here’s what Robert A. Smith, PhD, vice president of cancer screening at the American Cancer Society, said about that study:

Robert A. Smith, PhD
VP, Cancer Screening

“The most important takeaway from this and other studies of false positives and subsequent risk of breast cancer is that this information adds to the ability to estimate risk, and may help women and their doctors make decisions about screening moving forward. A prior false positive finding should be included in the factors considered as a woman decides on the frequency and types of screening she has as she ages.”

Recently updated recommendations from the American Cancer Society say starting at age 40, a woman should discuss with her doctor when to start screening, as long as she starts by age 45. The guideline points out that while the risk of breast cancer is lower in women between the ages of 40 to 44, some women will choose to accept the greater chance of a false positive as a reasonable trade-off for the benefits of screening.