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In September 2024, more than 40 million women who get annual mammograms in the United States began receiving information on their breast density because of a mandate from the US Food and Drug Administration (FDA). For the first time, a federal rule dictated that mammography centers were required to tell women whether their breasts were considered “dense,” a designation assigned to about half of all women in the US. Most states had previously established those requirements.

Authors of a paper published in JAMA Insights note that the FDA mandate “increases the complexity of breast cancer screening for women and their clinicians, many of whom may not be prepared to interpret and act on information about breast density.”

To help ease conversations with patients about breast density, Christoph I. Lee, MD, MS, with the Departments of Radiology and Health Systems and Population Health at the University of Washington, Seattle, and the Fred Hutchinson Cancer Center, and Joann G. Elmore, MD, MPH, with the David Geffen School of Medicine at University of California, Los Angeles, and professor at the UCLA Fielding School of Public Health, offer an evidence-based summary aimed at informing shared decision making. 

Three concepts dominate the summary:

• Women with dense breasts who don’t have other breast cancer risk factors should not be considered at high risk for breast cancer.
• Screening beyond routine mammography is not necessary for women with dense breasts at average risk for breast cancer.
• Deciding whether to order supplemental screening with breast MRI or ultrasonography should be based on a comprehensive risk assessment (not breast density alone) and should include patients’ values regarding risks and benefits of additional interventions.

Among the common questions the paper answers is whether breast density affects the accuracy of mammograms. The answer: “Digital mammography and digital breast tomosynthesis have high accuracy for detecting breast cancer, even for dense breasts (digital breast tomosynthesis sensitivity is [about] 88% for all women and 77% for women with dense breasts).”

The paper also addresses benefits and harms of supplemental screening.

Lee and Elmore note that no randomized trials to date have shown a reduction in breast cancer deaths when MRI or ultrasound screening is added after a mammogram for asymptomatic women with dense breasts.

But there can be harms for supplemental screening. Ultrasonography screening after a woman with dense breasts has a negative mammogram “likely leads to greater harms than benefits,” the authors write. They point to a population-based modeling study that suggests adding supplemental ultrasonography every other year for women 50-74 years old with dense breasts who had previous negative mammograms “would result in 354 additional biopsy recommendations per 1000 women compared with biennial mammography alone, while only preventing 0.36 additional cancer deaths per 1000 women with dense breasts.”

A comparative effectiveness analysis published in 2024 estimated that adding MRI to digital breast tomosynthesis for all US women ages 40-74 years with dense breasts who underwent screening every other year over 3.5 decades “would lead to more lives saved (9.5 vs 8.5 per 1000 women screened) but increased the number of false-positive results (1850 compared with 1392 per 1000 women screened) and benign biopsies (628 vs 221 per 1000 women screened).

However, the authors add, supplemental screening for women at high risk for breast cancer (more than 20% lifetime risk) can be offered.

Harms from false-positive imaging and benign biopsy results may include patient anxiety, discomfort, and financial burden, the authors note.

Dr. Lee receives funding in part from the National Cancer Institute for breast cancer-related research and reported receiving personal fees from the American College of Radiology for journal editorial board work and DeepHealth/RadNet for research consulting and royalties from McGraw Hill, Oxford University Press, and UpToDate outside the submitted work. Dr. Elmore receives funding in part from the National Cancer Institute for breast cancer-related research and reported receiving personal fees from UpToDate. 

Journalist bio here Marcia Frellick is an independent healthcare journalist based in Chicago.