Study quantifies false positives for yearly mammograms

Breast Cancer Surveillance Consortium also compares digital and film mammography

The Breast Cancer Surveillance Consortium (BCSC), a National Cancer Institute-funded research resource and collaborative network, published two studies today in the journal Annals of Internal Medicine that may help women make decisions about how frequently to have a mammogram and what types of mammography facilities are best.

The BCSC focuses on studies designed to assess the delivery and quality of breast cancer screening and related patient outcomes in the United States and includes a collaborative network of seven mammography registries with linkages to tumor and/or pathology registries.

Bonnie Yankaskas, PhD, a professor in the UNC department of radiology and a member of UNC Lineberger Comprehensive Cancer Center is a co-author on both studies.

One study sought to quantify the number of false positives – instances when a women without breast cancer is called back after screening mammography for extra testing – in two instances.  First, when comparing women who had annual mammograms compared to those who had the test every other year and second, comparing women who started annual mammograms at age 50 compared to age 40.

The researchers found that screening every other year lowered the probability of having a false positive over the course of 10 years by approximately one-third (from 61 percent to 42 percent).  Having prior mammograms available for comparison cut the odds of false positives in half.  The research team encouraged women who are not having their screenings at the same facility to arrange in advance to have their previous mammograms sent to the new facility.  The team also found that, among women who were diagnosed with cancer, those screened with a two-year interval were not significantly more likely to be diagnosed with late-stage cancer compared to those screened with a one-year interval.

The team encourages women to talk with their doctors to make informed decisions about how often is best for them to get screening and when to start, since mammography is the only screening test proven in clinical trials to reduce women’s risk of dying of breast cancer.  The motivation for the study was to quantify false positives, since a false positive result can be a stressful experience that might be a barrier to women getting regular screening mammograms.

In a second study published in the same journal, the research team assessed the accuracy of digital compared to film mammography in U.S. community practice.  The researchers found that both types of mammograms performed similarly for women age 50-79 for detecting cancer.  But for women in their 40s who have not gone through menopause and who have dense breasts, digital mammography may be better than film mammography at detecting cancer.  At the same time, for women aged 40-49 the risk of false positives was somewhat higher with digital than with film mammography.

In addition to Dr. Yankaskas, the other co-authors of both studies were Rebecca Hubbard, PhD, and Diana Miglioretti, PhD, of Group Health Research Institute, and Karla Kerlikowske, MD, of the University of Califonia, San Francisco.

Other co-authors of the false positive study were Weiwei Zhu, MS of Group Health Research Institute and Chris Flowers, MD, of the Moffitt Cancer Center and Research Institute.  Additional co-authors of the digital vs. film mammography study were Constance Lehman, MD, PhD, of the University of Washington and Group Health Research Institute, Berta Geller, EdD, of the University of Vermont, Stephen Taplin, MD, MPH, of the National Cancer Institute, and Edward Sickles, MD, of the University of California, San Francisco.

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