What imaging is recommended for patients with heterogeneously dense breasts categorized as category C (Breast Imaging-Reporting and Data System - BI-RADS)?

Supplemental Imaging for Heterogeneously Dense Breasts (BI-RADS Category C)

For women with heterogeneously dense breasts (BI-RADS category C), digital breast tomosynthesis (DBT) should be used as the primary screening method, with breast MRI or abbreviated breast MRI (AB-MRI) as the preferred supplemental screening option to maximize cancer detection. 1

Understanding Breast Density and Its Impact

• Heterogeneously dense breast tissue (BI-RADS category C) reduces mammographic sensitivity to as low as 63% compared to 87% in fatty breasts, significantly impairing cancer detection 1
• Dense breast tissue is an independent risk factor for breast cancer development, with heterogeneously dense breasts associated with a relative risk of 1.23-1.30 for developing invasive breast cancer compared to women with average breast density 1
• Approximately half of screening-aged women in the United States have dense breast tissue (heterogeneously or extremely dense), requiring consideration of supplemental screening options 1, 2

Recommended Primary Screening Approach

• Digital Breast Tomosynthesis (DBT) should be used as the primary screening method for women with heterogeneously dense breasts, as it shows improved cancer detection rates compared to conventional 2D mammography 1
• DBT demonstrates the greatest increase in cancer detection rate specifically in women with heterogeneously dense breasts (BI-RADS category C) compared to other density categories 1
• DBT offers the additional benefit of reduced recall rates (15-63% reduction) and improved specificity compared to conventional mammography 1

Recommended Supplemental Screening Options

First-Line Supplemental Option: Breast MRI or Abbreviated Breast MRI

• Breast MRI or abbreviated breast MRI (AB-MRI) is the preferred supplemental screening option for women with heterogeneously dense breasts due to superior cancer detection rates 1
• AB-MRI demonstrated a cancer detection rate of 15.2 per 1,000 examinations compared to only 6.2 per 1,000 with DBT alone in women with dense breasts 1
• Cancers detected by MRI tend to be smaller, lymph node negative, and less biologically aggressive, potentially improving outcomes 1, 2
• The DENSE trial showed supplemental MRI reduced interval cancer rates from 5.0 to 0.8 per 1,000 screenings in women with extremely dense breasts, suggesting a mortality benefit that likely extends to heterogeneously dense breasts 1, 3

Alternative Supplemental Option: Whole Breast Ultrasound

• Whole breast ultrasound (WBUS) may be considered when MRI is not available or contraindicated 1
• Screening ultrasound can detect an additional 4.2 cancers per 1,000 women with dense breasts that are not visible on mammography 4
• However, ultrasound has significant limitations including higher false-positive rates, lower positive predictive values for biopsies, and high rates of short-term follow-up recommendations 1, 5
• No added benefit of screening ultrasound has been found in women who undergo MRI or AB-MRI screening 1

Implementation Considerations

• The FDA now requires that women be notified of their breast density status and informed that supplemental imaging may be beneficial 1, 2
• Risk assessment should be performed for all women by age 25 to better stratify screening recommendations beyond breast density alone 2
• First-round supplemental MRI screening may result in higher false-positive rates (79.8 per 1,000 screenings), but these rates decrease substantially in subsequent screening rounds 1, 3
• For women unable to undergo MRI due to contraindications or access issues, whole breast ultrasound provides a viable alternative despite its limitations 5, 6

Emerging Options

• Contrast-enhanced mammography (CEM) is showing promise as a supplemental screening tool for women with dense breasts, with cancer detection rates ranging from 8.6 to 13.1 per 1,000 examinations 1
• The CMIST trial is currently comparing DBT and CEM in women with dense breasts, which may provide additional guidance in the future 1