Fibroglandular Density in Breasts

Dense Breast Tissue May Make Detecting Cancer Harder and Put Women at Higher Risk

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Download Breast Density: Breast Cancer Screening

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.

Breast density is determined by the radiologist who reads a woman’s mammogram. There are four categories of density determined by a mammogram. The radiologist assigns each mammogram to one of the categories. The woman’s doctor should be able to determine whether she has dense breasts based on where she falls on the density scale.

The four levels of breast density are:

  • Almost entirely fatty
  • Scattered areas of fibroglandular density
  • Heterogeneously dense
  • Extremely dense

Radiologists classify breast density using a 4-level density scale:

Breast Density Almost Entirely Fatty
Almost entirely fatty
Breast Density Scattered Areas of Fibroglandular Density
Scattered areas of fibroglandular density
Breast Density Heterogeneously Dense
Heterogeneously dense
Breast Density Extremely Dense
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
Breast Density Distribution

Why Is Breast Density Important?

Having dense breast tissue may increase a woman’s chance of getting breast cancer. Dense breasts also make it more difficult for doctors to spot cancer on mammograms. Dense tissue appears white on a mammogram; lumps, both benign and cancerous, also appear white. So, mammograms can be less accurate in women with dense breasts.

If a woman’s mammogram shows she has heterogeneously dense or extremely dense breast tissue, she will receive a letter notifying her that she has dense breasts. She can then speak to her primary care physician about what this means for her and what, if any, additional tests she may need.