There will always be some healthy people who mistakenly test positive when tested for disease. Although we have heard a great deal during the last few years about false positive mammograms and the unnecessary distress, diagnostic procedures, and cost they cause, there are other sides to this issue. One is the problem of false negatives, in which existing breast tumors are not found on screening mammograms. This causes some women to be diagnosed when their tumors are larger and at a later stage than they might have been.
The "false" false positive mammogram
Another problem is that some false positives are actually "false" false positives; the abnormality seen during screening and determined to be benign upon additional testing turns out to have been the beginnings of breast cancer after all. This is not a frequent occurrence and we do not mean to overemphasize it's significance. However, it does mean that women who are told that they do not have cancer after being called back for diagnostic mammograms or other additional testing should be diligent about getting screened annually thereafter. A new study has provided more information on the frequency and other characteristics of "false" false positives.
Study compared false positive with negative mammogram outcomes
The Danish study referenced at the beginning of this news article was designed to investigate the long-term risk of breast cancer among women with false positive screening mammograms. To conduct the study, the authors analyzed 1991 to 2005 data from a screening mammography program in Copenhagen. Women with false positive screening mammograms were compared to women with consistently negative mammograms.
A false positive test was defined as an abnormality seen in a screening mammography that was not confirmed by additional testing (normally consisting of a clinical examination, additional mammograms, and needle biopsy). The study included a total of 58,003 postmenopausal women (50 to 69 years old) who were followed for an average of 10.9 years. The analysis took into account age, screening round (women with a false positive finding in a previous round were excluded from analysis in subsequent rounds), and screening technology period (since recent advances have improved mammogram accuracy).
Women with solely negative mammograms were found to have a breast cancer rate of 339 per 100,000 person-years. On the other hand, women with a false positive mammogram had a rate of 583 per 100,000. Women with a false positive test had an adjusted risk of breast cancer that was 1.67 times that of women with negative mammograms. The risk remained elevated for at least six years after a false positive test.
When the results were analyzed according to the technology period, only the false positive group from the mid 1990s had a statistically significant higher risk of breast cancer than the group with negative tests. The authors conclude that the implementation of improved technology in the early 2000s reduced the size of excess risk of breast cancer for women with false positive screening results. This finding implies that the rate of false positives has declined as a result of improved technology.