San Francisco Study Reports Biennial Mammograms Better for Women 50 and Older, Including those with Dense Breast Tissue

A new national study finds that a screening for breast cancer every two years appears to be just as beneficial as yearly mammograms for women ages 50 to 74, with significantly fewer "false positives" or even for women whose breasts are dense who use hormone therapy for menopause, according to the journal JAMA Internal Medicine.

The study, researched by UC San Francisco and Seattle-based Group Health Research-based Group Health Institute, reported similar findings that involved more than 900,000 women ages 66 to 89.

By contrast, the study notes that women in their 40s with extremely dense breasts who undergo biennial mammography are more likely to have advanced-stage and large tumors than women who undergo annual mammography - but annual mammograms also resulted in more false positives, according to the new study from the Breast Cancer Surveillance Consortium (BCSC), the largest available screening mammography dataset in the United States. Having dense breasts means it is difficult for X-rays to pass through the breast tissue.

Approximately 12 to 15 percent of women in their 40s - and approximately 3 to 6 percent of those ages 50 to 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."

"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.

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

Cancer Institute-funded Breast Cancer Surveillance Consortium (U01 CA 63740, 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.