False positive results from screening mammograms help fuel the debate about the value of breast cancer screening. When a mammogram shows an abnormal area that looks like a cancer but turns out to be normal, it's called a false positive.
Ultimately the news is good: no breast cancer. But the suspicious area usually requires follow-up with one or more doctors, extra tests, and extra procedures, including a possible biopsy. There are psychological, physical, and economic costs that come with a false positive.
A large Danish study found that women who had a false positive mammogram result were more likely to be diagnosed with breast cancer in the future compared to women who never had a false positive result.
The results were published online April 5, 2012 in the Journal of the National Cancer Institute. Read the abstract of Risk of Breast Cancer After False-Positive Test Results in Screening Mammography.
Researchers looked at results from more than 58,000 women who had regular mammograms between 1991 and 2005. The women were age 50 to 69 and the mammograms were done through a national screening program. The women were followed for about 11 years.
False positives happened throughout the study, but the risk of a false positive went down in more recent years. In 1991, 5.6% of mammograms resulted in a false positive compared to 1.4% in 2005. This suggests that screening accuracy has improved.
Women who had a false positive mammogram result had a 67% higher risk of being diagnosed with breast cancer during the 6 to 12 years after the false positive compared to women who never had a false positive result. The results were reported in person-years, which takes into account the number of years each woman in the study was followed. For example, a woman who is followed for 10 years accounts for 10 person-years.
After the nearly 11 years of follow-up:
- 339 breast cancers were diagnosed over 100,000 person-years among women who never had a false positive
- 583 breast cancers were diagnosed over 100,000 person-years among women who had a false positive
The researchers aren't sure why women with a false positive mammogram result were more likely to be diagnosed with breast cancer. It's possible that factors that make a woman more likely to develop breast abnormalities that aren't cancer also make her more likely to develop breast cancer. For some women, it's also possible that even though the false positive wasn't cancer, the beginning of cancer was actually there and was found later. Whatever the reason for the link, the results suggest that a false positive mammogram result means a woman has a higher risk of being diagnosed with breast cancer in the future.
If you've had a false positive mammogram result, take extra care to get follow-up and ongoing breast cancer screening as recommended. You also might want to ask your doctor if a more aggressive breast cancer screening plan would make sense for you.
For more information on mammograms and other tests to detect breast cancer, visit the Breastcancer.org Breast Cancer Tests: Screening, Diagnosis, and Monitoring pages.