New federal mandate on breast density: Experts provide essential guidance for clinicians and patients

A new federal mandate requires that all women undergoing mammography in the U.S. be informed about their breast density—a factor that affects both cancer detection and risk. The regulation mandates that more than 40 million women receiving mammograms each year receive this information. 

While the regulation aims to improve patient awareness, it also presents challenges for clinicians and patients who may be unprepared to interpret and act on the information. 

“As more women receive breast density information under the new mandate, clear communication between patients and clinicians will be essential for informed decision-making in breast cancer screening and prevention,” said Joann Elmore, MD, MPH, a professor of medicine at the David Geffen School of Medicine at UCLA(Link is external) (Link opens in new window) and investigator at the UCLA Health Jonsson Comprehensive Cancer Center.

To help guide informed discussions between physicians and patients, Dr. Elmore and Christoph Lee, MD, MS, from the University of Washington School of Medicine, outline six key questions, published in JAMA(Link is external) (Link opens in new window), about breast density, including: 

1. What is breast density?

Breast density refers to the amount of fibrous and glandular tissue compared to fatty tissue in the breast, as seen on a mammogram. Radiologists classify breast density into four categories: almost entirely fatty, scattered fibroglandular densities, heterogeneously dense, and extremely dense (the latter two are considered dense). Thus, approximately half of all women are classified as having dense breasts. Dense breast tissue is a normal finding, but it can make cancer more difficult to detect. Patients are typically only informed whether their breasts are classified as dense or not. A recent study found that radiologists disagreed on the density classification in 17% of cases. While software can provide a more consistent measurement, it is not widely available, leaving radiologists to make the final determination.

2. Does breast density affect mammography?

While media and advocacy groups often emphasize that dense breast tissue can make it harder to detect cancer, modern imaging techniques have improved detection. Both digital mammography and digital breast tomosynthesis, or 3D mammography, are effective at finding breast cancer, even in women with dense breasts. 3D mammography can detect about 77% of breast cancers in women with dense breasts, and up to 88% among all women. While slightly less accurate in dense tissue, mammography remains the most valuable screening tool available.

3. How much does breast density increase breast cancer risk?

While dense breast tissue is linked to a higher chance of developing breast cancer, it doesn’t necessarily mean a woman is at high risk. For women in their 40s with dense breasts, the risk is similar to having a second degree relative, like an aunt or grandmother, with breast cancer or having had a benign breast biopsy in the past. Doctors generally define high risk as having a greater than 20% lifetime risk of breast cancer, based on multiple factors. Most women with dense breasts still fall into the average-risk category. On the other hand, some women with non-dense breasts may be at high risk due to other factors, such as carrying a BRCA1 or BRCA2 gene mutation or having a first-degree family member, like a mother or sister, diagnosed with breast or ovarian cancer at a young age. Rather than focusing only on breast density in shared-decision making discussions, clinicians should consider it alongside other risk factors when discussing screening and prevention options.

4. What are risk prediction tools for assessing a woman’s risk of breast cancer?

All women can benefit from a more thorough risk assessment to understand their chances of developing breast cancer. Risk prediction tools, like the Tyrer-Cuzick model(Link is external) (Link opens in new window), the Breast Cancer Risk Assessment Tool(Link is external) (Link opens in new window), and the Breast Cancer Surveillance Consortium Risk Calculator(Link is external) (Link opens in new window), estimate a woman’s likelihood of developing breast cancer over five years, 10 years, and/or over a lifetime. These risk estimates can help doctors recommend additional screening, such as breast MRIs, or preventive treatments, like tamoxifen or raloxifene, for women at higher risk.

5. Should supplemental screening be recommended?

For most women, having dense breast tissue alone should not automatically trigger additional screening beyond a mammogram. However, women with a high lifetime risk based on a more comprehensive risk assessment may benefit from supplemental screening. Breast MRI is the preferred option for high-risk individuals, detecting more cancers with a sensitivity of over 80%, compared to about 55% for ultrasound after a negative mammogram. Ultrasound is an alternative for those who cannot undergo an MRI or do not have access to one. 

6. What are the benefits and harms of supplemental screening?

Supplemental screening, such as MRI, can help detect breast cancer earlier, which may improve clinical outcomes. However, it also comes with potential downsides. Additional tests can lead to anxiety from false-positive results, discomfort from unnecessary biopsies, and increased costs from additional diagnostic evaluation, interventions, and treatments for indolent cancers that may never have caused harm.

"Understanding breast density is just one piece of the puzzle in breast cancer screening,” said Dr. Elmore. “By combining this information with a woman’s overall risk profile, clinicians can better guide patients in making personalized, informed choices about their health."