Women with Dense Breasts May Not Need More Screening

As the debate continues to swirl around the medical significance of dense breasts and whether extra screening should be done, a new study led by UC San Francisco has found that women with dense breasts may need only routine mammograms unless they are at high risk.

In their paper, the researchers said that five-year breast cancer risk is a critical component, and breast density should not be the sole factor in deciding whether supplemental screening is justified because not all women with dense breasts are at high risk of cancer. 

Research has shown that women with dense breasts may be more likely to develop cancer.

The study was published May 18 in Annals of Internal Medicine.

The research focused on approximately 365,000 women ages 40 to 74 years old who had undergone a regular digital screening mammogram and had no history of breast implants or breast cancer.  

Breast density is determined only by mammograms – having dense breasts makes it more difficult for X-rays to pass through the breast tissue and can mask tumors. Breasts are considered dense if the woman has a lot of fibrous or glandular tissue but not much fatty tissue, according to the American Cancer Society.

“Not all women with dense breasts have a high-enough risk of cancer to justify supplemental screening,” said lead author, Karla Kerlikowske, MD, a professor of medicine and epidemiology and biostatistics at UCSF and a primary care physician at the UCSF-affiliated San Francisco VA Medical Center. “We found that for the vast majority of women undergoing mammography – including those with dense breasts but low five-year breast cancer risk – the chance of developing breast cancer within 12 months of a normal mammogram was low. Women with extremely dense breasts and intermediate to high five-year breast cancer or heterogeneously dense breasts and high five-year breast cancer risk were at highest risk for developing breast cancer after a normal mammogram.”

“Our findings can help guide women and providers in discussing supplemental imaging and whether to consider extra testing,” said Kerlikowske. “This study provides a starting point to identify women who may have the most to gain from supplemental imaging or alternative imaging strategies.” 

Issues with Supplemental Imaging for Dense Breasts

Currently, 22 states require that women be notified if they have dense breasts. The laws also encourage women to discuss supplemental screening with their medical providers. Similar legislation, which would set a minimum standard for notification and recommend that women discuss with their doctors whether further screening is necessary, is pending in Congress which would have a considerable impact nationally, affecting tens of millions of women annually.

Digital mammography, used by the vast majority of mammography facilities, detects 81 to 87 percent of breast cancers among women 40 to 79 years old, reported the authors. But its ability to detect breast cancer in women with extremely dense breasts is lower. 

As a result, supplemental imaging has been suggested for women with dense breasts to heighten their chances for tumor detection before women become symptomatic. While supplemental imaging for women with dense breasts can increase cancer detection, it can also lead to more false-positive results and more unnecessary biopsies.

Calculating Risks

In the prospective cohort study drawing upon statistics from 2002 to 2011, the researchers analyzed screening data collected by the Breast Cancer Surveillance Consortium (BCSC). Overall, nearly half the women in the study had dense breasts, and the proportion with heightened five-year risk was highest among those with extremely dense breasts.

“We found that rather than using only breast density to decide whether women with dense breasts should be considered for supplemental imaging, breast cancer risk should be taken into consideration,” said Kerlikowske, a member of the breast oncology program at the UCSF Helen Diller Family Comprehensive Cancer Center. “The BCSC risk calculator that includes age, family history of breast cancer, history of breast biopsy, breast density and race can be used to calculate five-year breast cancer risk. Determining breast cancer risk along with knowing a woman’s breast density will optimize the identification of women with high interval cancer rates who may benefit from supplemental screening.”

The authors noted that they were unable to assess the benefits of patient discussions with providers about supplemental breast imaging.

Co-authors are Weiwei Zhu, MS, a biostatistician at the Group Health Cooperative in Seattle and the University of Washington School of Medicine; Anna N.A. Tosteson, ScD, a professor of medicine at The Dartmouth Institute; Brian L. Sprague, PhD, an assistant professor of surgery at the University of Vermont Cancer Center; Jeffrey A. Tice, MD, a UCSF associate professor of medicine and member of the UCSF Helen Diller Family Comprehensive Cancer Center; Constance D. Lehman, MD, PhD, a professor at the University of Washington School of Medicine and vice chair of radiology; and  Diana L. Miglioretti, PhD, a professor of biostatistics at UC Davis and co-leader of the Breast Cancer Surveillance Consortium. 

The research was supported by the National Cancer Institute-funded Breast Cancer Surveillance Consortium (P01 CA154292, HHSN261201100031C and U54 CA163303). The collection of cancer data used in the study was supported in part by several state public health departments and cancer registries in the U.S.  

UCSF is the nation's leading university exclusively focused on health. Now celebrating the 150th anniversary of its founding as a medical college, UCSF is dedicated to transforming health worldwide through advanced biomedical research, graduate-level education in the life sciences and health professions, and excellence in patient care. It includes top-ranked graduate schools of dentistry, medicine, nursing and pharmacy; a graduate division with world-renowned programs in the biological sciences, a preeminent biomedical research enterprise and top-tier hospitals, UCSF Medical Center and UCSF Benioff Children's Hospitals.