March 18, 2013

Biennial mammograms best for ages 50–74, even with dense breasts

More benefit—and harm—from annual screening in 40s with extremely dense breasts, BCSC finds

Seattle, WA—Screening for breast cancer every two years appears just as beneficial as yearly mammograms for women age 50–74, with significantly fewer “false positives”—even for women whose breasts were dense or who used hormone therapy for menopause. So found a Breast Cancer Surveillance Consortium (BCSC) study, including researchers from UC San Francisco (UCSF) and Group Health. The national study of more than 900,000 women is in JAMA Internal Medicine. The same research team recently reported similar results for older women (age 66-89).

By contrast, for women in their 40s who had extremely dense breasts, a yearly schedule resulted in fewer advanced-stage and large tumors being found—although also in more false positives, according to the same new study from the BCSC, the largest available screening mammography data set in the United States. Having dense breasts means it’s difficult for X-rays to pass through the breast tissue, and that doesn’t correlate with how firm the breast feels.

“Increasing age and high breast density are among the strongest risk factors for the disease,” said senior author Karla Kerlikowske, MD, a professor of medicine at UCSF and a physician at the UCSF-affiliated San Francisco VA Medical Center. She and other BCSC researchers reported in 2012 that risk factors may inform the individual decisions that women make with their doctors about when to start breast cancer screening and how often to repeat it. For instance, a family history of breast cancer raises the likelihood of developing the disease—but not of advanced-stage or large tumors.

“These individual decisions involve evaluating the balance between the benefits of screening—detecting cancer early—and the potential harms, such as false positives among healthy women,” Dr. Kerlikowske added. False positives mean that women without cancer are called back for more testing, including biopsies and more mammograms and ultrasounds. “Some people who are at higher risk of disease may be more willing than those at lower risk to accept such potential harms of screening, but again, it’s an individual decision,” she added.

“For women 50-74 with dense breasts who are cancer free, we estimated that more than half will be recalled for additional mammography at least once over the course of 10 years of annual screening,” said coauthor Rebecca A. Hubbard, PhD, an assistant investigator at Group Health Research Institute who is also at the University of Washington School of Public Health. “Screening every other year decreases this risk by about a third. The risk of false-positive results is even higher for women who begin screening at age 40.”

When the U.S. Preventive Services Task Force updated its breast cancer screening guidelines in 2009, it advised women to make individual decisions with their doctors. But for average-risk women, these guidelines advised screening mammography every two years for women aged 50 to 74. The guidelines recommended that women in their 40s consider their personal values regarding the benefits and harms and then decide when to begin regular screening. The Task Force deemed evidence on risk factors other than age to be weak at that point.

The new study was designed to explore other risk factors for breast cancer, beyond age. Extremely dense breasts and taking combination hormone therapy (with estrogen and progestin, although not with estrogen alone) had already been shown to raise women’s rates of advanced-stage or large tumors.

Around 12–15 percent of women in their 40s—and around 3–6 percent of those age 50–74—have extremely dense breasts. How does a woman know if her breasts are dense—or extremely dense? “It’s a Catch-22,” said co-author Diana L. Miglioretti, PhD, a senior investigator at Group Health Research Institute, who is also at the University of California at Davis. “The only standard way to determine your level of breast density is to get a mammogram—but unless your breasts are extremely dense and you have other strong risk factors, the data don’t necessarily support your starting screening mammograms before age 50.”

Drs. Kerlikowske, Hubbard, and Miglioretti’s co-authors were:

  • At Group Health Research Institute: Assistant Investigator Karen J. Wernli, PhD; Research Associate Ellen S. O'Meara, PhD; and Biostatistician Weiwei Zhu, MS
  • At UCSF, Dejana Braithwaite, PhD
  • And at the University of Vermont, Berta Geller, EdD, and Kim Dittus, MD, PhD.

The study was supported by grants from the National Cancer Institute of the National Institutes of Health (R03 CA150007, RC2 CA148577, and P01 CA107584), the National Cancer Institute-funded Breast Cancer Surveillance Consortium (U01 CA63740, CA86076, CA86082, CA63736, CA70013, CA69976, CA63731, and CA70040. Several state public health departments and cancer registries throughout the United States supported, in part, the collection of cancer data used in this study.

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, including women from Group Health Cooperative, San Francisco Mammography Registry, Carolina Mammography Registry, Colorado Mammography Project, New Hampshire Mammography Network, New Mexico Mammography Project, and Vermont Breast Cancer Surveillance System. The network is supported by a central Statistical Coordinating Center.

UC San Francisco

UC 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.

About Kaiser Permanente

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Karen Wernli, PhD

Associate Investigator
Kaiser Permanente Washington Health Research Institute

Weiwei Zhu, MS

Biostatistician III
Kaiser Permanente Washington Health Research Institute

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