October 17, 2011

Yearly mammograms? Expect a ‘false positive’ each decade

Annals of Internal Medicine publishes Group Health-led national study

Seattle, WA—In 10 years of annual mammograms, more than half of women without cancer will be called back at least once for more testing. And about one in 12 will be referred for a biopsy, according to a study of national Breast Cancer Surveillance Consortium data in the Annals of Internal Medicine. Here’s the journal’s summary for patients.

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Watch a video about a Group Health-led national study concerning mammography and false positives

Rebecca Hubbard, PhD“We conducted this study to help women know what to expect when they get regular screening mammograms over the course of many years,” said study leader Rebecca Hubbard, PhD, an assistant investigator at Group Health Research Institute. “We hope that if women know what to expect with screening, they’ll feel less anxiety if—or when—they are called back for more testing. In the vast majority of cases, this does not mean they have cancer.” When a woman without breast cancer is called back after screening mammography for extra testing, she has a “false positive.”

“We wanted to understand better how likely false-positive test results are when women receive annual screening mammograms compared to every other year—and starting at age 50 compared to age 40,” Dr. Hubbard said. She and her team examined data from more than 169,000 women aged 40-59 at seven regions around the United States.

Screening every other year, instead of yearly, lowered women’s probability of having a false positive over the course of 10 years by about a third—from 61 percent to 42 percent, Dr. Hubbard said. Having prior mammograms available for comparison cut the odds of false positives in half. So if women aren’t returning to the same mammography facility, they should arrange in advance to have their previous mammograms sent to the new facility.

“We found that women in their 40s and 50s had similar risks of having a false positive during 10 years of screening,” she added. “But over the course of a lifetime, starting screening at age 40 would make a woman more likely to have false positives than if she had started at age 50, because of that extra decade of screening.”

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. “Women should talk with their doctors to make informed decisions about how often is best for them to get screening—and when to start,” Dr. Hubbard said.

Mammography is the only screening test proven in clinical trials to reduce women’s risk of dying of breast cancer. Having a false positive can be a stressful experience, and it might be a barrier to women getting regular screening mammograms.

An accompanying Breast Cancer Surveillance Consortium study in the same issue of Annals, led by Karla Kerlikowske, MD, of the University of California, San Francisco, is the first to assess the accuracy of digital compared to film mammography in U.S. community practice. Over the past few years, newer digital mammography has been replacing older film mammography.

The researchers, including Dr. Hubbard, found that both types of mammograms—digital and film—performed similarly for women age 50 to 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. But in women age 40-49, the risk of false positives was somewhat higher with digital than with film mammography.

An accompanying editorial, from the International Prevention Research Institute in Lyon, France, puts the two studies in context.

The National Cancer Institute, which supports the Breast Cancer Surveillance Consortium, funded both studies. The collection of cancer data was also supported in part by several state public health departments and cancer registries throughout the United States.

Diana Miglioretti, PhD
D. Miglioretti  

Weiwei Zhu, MS
W. Zhu

In addition to Drs. Hubbard and Kerlikowske, the other co-authors of both studies were Diana L. Miglioretti, PhD, of Group Health Research Institute and Bonnie C. Yankaskas, PhD, of the University of North Carolina at Chapel Hill.

In addition to Drs. Hubbard, Kerlikowske, Miglioretti, and Yankaskas, the other co-authors of the study on false positives were Weiwei Zhu, MS, of Group Health Research Institute and Chris I. Flowers, MD, of the Moffitt Cancer Center and Research Institute, in Tampa, FL.

And the other co-authors of the study on digital vs. film mammography were Constance D. Lehman, MD, PhD, of the University of Washington, also an affiliate investigator at Group Health Research Institute; Berta M. Geller, EdD, of the University of Vermont in Burlington; Stephen H. Taplin, MD, MPH, of the National Cancer Institute; and Edward A. Sickles, MD, of the University of California, San Francisco.

Group Health Research Institute
Group Health Research Institute does practical research that helps people like you and your family stay healthy. The Institute is the research arm of Seattle-based Group Health Cooperative, a consumer-governed, nonprofit health care system. Founded in 1947, Group Health Cooperative coordinates health care and coverage. Group Health Research Institute changed its name from Group Health Center for Health Studies in 2009. Since 1983, the Institute has conducted nonproprietary public-interest research on preventing, diagnosing, and treating major health problems. Government and private research grants provide its main funding.

Breast Cancer Surveillance Consortium
The Breast Cancer Surveillance Consortium (BCSC) is the nation's largest and most comprehensive collection of breast cancer screening information. It’s a research resource for studies designed to assess the delivery and quality of breast cancer screening and related patient outcomes in the United States. The BCSC is a National Cancer Institute-funded collaborative network of seven mammography registries with linkages to tumor and/or pathology registries. The network is supported by a central Statistical Coordinating Center. Currently, the Consortium's database contains information on over 9.5 million mammographic examinations, 2.3 million women, and 114,000 breast cancer cases (95,000 invasive cancers and 19,000 ductal carcinoma in situ). For more information, visit http://breastscreening.cancer.gov.

University of California, San Francisco
The University of California, San Francisco (UCSF) is a leading university dedicated to promoting health worldwide through advanced biomedical research, graduate-level education in the life sciences and health professions, and excellence in patient care. It is the only campus in the 10-campus UC system dedicated exclusively to the health sciences. For more information, visit http://www.ucsf.edu.

Annals of Internal Medicine
Established in 1927 by the American College of Physicians (ACP), Annals of Internal Medicine is the premier internal medicine journal. Annals of Internal Medicine’s mission is to promote excellence in medicine, enable physicians and other health care professionals to be well informed members of the medical community and society, advance standards in the conduct and reporting of medical research, and contribute to improving the health of people worldwide. To achieve this mission, the journal publishes a wide variety of original research, review articles, practice guidelines, and commentary relevant to clinical practice, health care delivery, public health, health care policy, medical education, ethics, and research methodology. In addition, the journal publishes personal narratives that convey the feeling and the art of medicine. For more information, see http://www.annals.org.