North American mammographers prone to more false positives, study finds

September 16, 2003

Community-based mammography screening programs in North America are yielding a higher percentage of abnormal mammograms than corresponding programs in other countries, but without any apparent benefit in terms of a higher cancer detection rate, according to a study in the September 17 issue of the Journal of the National Cancer Institute.

"This finding suggests that many, if not most, of the presumptively abnormal mammographic interpretations in screening programs with high percentages of abnormal mammograms turn out to be false positives," say study leader Joann G. Elmore, M.D., of the Harborview Medical Center in Seattle, and her colleagues. False-positive mammograms can lead to unnecessary follow-up procedures (e.g., biopsies), higher medical costs, and anxiety for the patient.

Elmore and her colleagues analyzed data from 32 studies of community-based screening mammography programs to compare outcomes of mammographic readings between programs in North America and those in other countries. In each study, they looked at the percentage of mammograms considered abnormal, the percentage of women diagnosed with ductal carcinoma in situ (DCIS), and the percentage of women diagnosed with minimal disease.

The percentage of mammograms deemed abnormal by North American programs was 2 to 4 percentage points higher than it was in programs in other countries, even after adjusting for factors such as age of women screened and number of mammography readers for each examination (single vs. double). North American programs also reported a higher percentage of DCIS. However, a higher percentage of abnormal mammograms did not appear to be associated with a higher rate of breast cancers being diagnosed.

The authors stress caution in interpreting these findings. They explain that a number of factors may be contributing to the observed variation between North American programs and programs in other countries, including differences in the population of women screened, differences in the screening procedure, and differences in how countries define an abnormal mammogram. Malpractice concerns and financial incentives may also be contributing to the variation in mammography interpretations, they say.

"Currently, it is not possible to determine which features may be most responsible for the variability," the authors write, adding that "a better understanding of the sources of variability in mammography may lead to more effective screening programs that have a lower percentage of mammograms judged as abnormal without substantially lowering the cancer detection rate."
Contact: Susan Gregg-Hanson, University of Washington Harborview Medical Center, 206-731-6397,

Elmore JG, Nakano CY, Koepsell TD, Desnick LM, D'Orsi CJ, Ransohoff DF. International variation in screening mammography interpretations in community-based programs. J Natl Cancer Inst 2003;95:1384-93.

Note: The Journal of the National Cancer Institute is published by Oxford University Press and is not affiliated with the National Cancer Institute. Attribution to the Journal of the National Cancer Institute is requested in all news coverage.

Journal of the National Cancer Institute

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