What Is Breast Density?
Breast density reflects the amount of fibrous and glandular tissue in a woman’s breasts compared with the amount of fatty tissue in the breasts, as seen on a mammogram.
On a mammography report, breast density is assigned to one of the following four categories—
- The breasts are almost entirely fatty (about 10% of women).
- A few areas of dense tissue are scattered through the breasts (about 40% of women).
- The breasts are evenly dense throughout (about 40% of women). This may be called “heterogeneously dense” on the mammography report.
- The breasts are extremely dense (about 10% of women).
Women in the first two categories are said to have low-density, non-dense, or fatty breasts. Women in the second two categories are said to have high-density or dense breasts. About half of women who are 40 years old or older have dense breasts.
Why Is Breast Density Important?
The image on the left shows a mostly fatty breast, and the image on the right shows a dense breast.
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Breast Cancer Risk
Women with dense breasts have a higher chance of getting breast cancer. The more dense your breasts are, the higher your risk. Scientists don’t know for sure why this is true.
Breast cancer patients who have dense breasts are not more likely to die from breast cancer than patients with non-dense (fatty) breasts.
Mammograms
Dense tissue can hide cancers. Fibrous and glandular tissue looks white on a mammogram. So does a possible tumor. Because it’s hard to tell the difference between a tumor and dense breast tissue on a mammogram, a small tumor may be missed.
Who Is More Likely to Have Dense Breasts?
The density of your breasts can change over time. Generally, you’re more likely to have dense breasts if you—
- Are younger.
- Are pregnant or breastfeeding.
- Are taking hormone replacement therapy.
- Have a lower body weight.
What Should I Do If I Have Dense Breasts?
Talk to your doctor about your personal risk of getting breast cancer. Dense breasts are just one of several risk factors for breast cancer. Your doctor will also think about other factors, like your age and family history of cancer.
Different tests may be able to find some cancers that are missed on a mammogram. But these tests are more likely to have a false positive result (the test is reported as abnormal, but you really don’t have cancer). False positive test results often lead to unnecessary tests, like a biopsy. Also, you may have to pay for these tests.
Your doctor may suggest one of these tests—
- Breast ultrasound. A machine that uses sound waves to make pictures, called sonograms, of areas inside the breast.
- Breast magnetic resonance imaging (MRI). A kind of body scan that uses a magnet linked to a computer. The MRI scan makes detailed pictures of areas inside the breast.
Talk with your doctor about how often you should be screened for breast cancer and which tests your doctor recommends.
More Information
- Dense Breasts: Answers to Commonly Asked Questions (National Cancer Institute)
- Breast Density and Your Mammogram Report (American Cancer Society)
- Dense Breast Tissue: What It Means to Have Dense Breasts (Mayo Clinic)
