Dense Breast Tissue

What is Dense Breast Tissue?

Breasts are made up of a mixture of fibrous and glandular tissue and fatty tissues. A woman’s breasts are considered dense if she has a lot of fibrous or glandular tissue, but not much fat. Density may decrease with age, but there is little, if any, change in most women.

Radiologists classify breast density using a four-level density scale, as determined by a mammogram:

• Category A: Almost entirely fatty
• Category B: Scattered areas of dense breast tissue
• Category C: Heterogeneously dense
• Category D: Extremely dense

Category A: Almost entirely fatty

Category B: Scattered areas of dense breast tissue

Category C: Heterogeneously dense

Category D: Extremely dense

In the U.S., breast density is distributed as follows:

• 10 percent of women have almost entirely fatty breasts
• 10 percent have extremely dense breasts
• 80 percent are classified into one of the two middle categories

Determining Breast Density

Dense breast tissue is determined by the radiologist who reads a mammogram. The radiologist assigns each mammogram to one of the four categories of breast density. If your mammogram shows that you have heterogeneously dense or extremely dense breast tissue, you will receive a letter notifying you that you have dense breasts. You can speak to your primary care physician about your risk and your breast cancer screening options.

Mammograms and Other Tests for Dense Breasts

Women with dense breasts should continue to receive a mammogram every year. Even though it may be harder to detect, a mammogram is still the best way to detect breast cancer in dense breasts. Additional tests if needed, may include:

• Tomosynthesis (3-D mammography)
• Breast ultrasound
• Breast magnetic resonance imaging (MRI)

Screening Tests for Dense Breasts