Breast Density on a Mammogram
What is breast density?
Breast density is a measure used to describe mammogram images. It’s not a measure of how the breasts feel.
Breasts are made up of breast tissue (the milk ducts and lobules, which may be called glandular tissue) and fat. Connective tissue helps hold everything place. Learn more about breast anatomy.
Breast density compares the area of breast and connective tissue seen on a mammogram to the area of fat. Breast and connective tissue are denser than fat and this difference shows up on a mammogram (see images below).
- High breast density means there’s more breast and connective tissue compared to fat.
- Low breast density means there’s more fat compared to breast and connective tissue.
By looking at your mammogram or the measure of breast density, your health care provider may conclude you have dense breasts.
How does dense breast tissue look on a mammogram?
The mammogram images below show a range of breast density. Some breasts are mostly fat (fatty breasts) and some breasts are mostly breast and connective tissue (dense breasts).
Mammograms of dense breasts are harder to read than mammograms of fatty breasts.
Learn more about breast density and mammography.
Breast density and breast cancer risk
Women with dense breasts are 4-5 times more likely to get breast cancer than women with fatty breasts [104-105].
Read our perspective on breast density and breast cancer risk.*
What affects breast density?
High breast density is common. In the U.S., 40-50 percent of women ages 40-74 have dense breasts [106-107].
Breast density varies greatly by age and weight. Dense breasts are more common in both young women and thin women [106-107]:
- About 50-60 percent of women ages 40-44 have dense breasts, compared to 20-30 percent of women ages 70-74.
- About 50-60 percent of women with a healthy weight have dense breasts, compared to 20-30 percent of obese women.
Medications that contain hormones can also affect breast density. For example :
- Women who take menopausal hormone therapy (MHT) tend to have denser breasts than they would if they didn’t take MHT. As women age, their breasts become less dense and more fatty. Taking MHT slows this process. MHT is also called postmenopausal hormone use and hormone replacement therapy (HRT).
- Women who take the drug tamoxifen (for treatment or for risk reduction) tend to have lower breast density than they would if they didn’t take tamoxifen.
Breast density legislation
Many states in the U.S. have laws requiring health care providers to notify (send a letter to) women found to have dense breasts on a mammogram. In 2019, the U.S. Congress passed national breast density legislation. The Food and Drug Administration (FDA), which regulates mammography centers, is developing regulations for notification.
Although this may seem helpful, there are no special recommendations or screening guidelines for women with dense breasts.
Although women with dense breasts have an increased risk of breast cancer, it’s not clear that lowering breast density will decrease risk. For example, getting older and gaining weight after menopause are both related to a decrease in breast density, but an increase in breast cancer risk.
If you have any concerns about your breast density or your risk of breast cancer, talk with your health care provider.
Screening for women with dense breasts
Dense breast tissue can make abnormal findings hard to see on a mammogram.
There are no special recommendations or screening guidelines for women with dense breasts. However, your health care provider may suggest other types of breast imaging.
Learn more about breast cancer screening.
3D mammography (breast tomosynthesis), breast ultrasound and breast MRI
Some data suggest 3D mammography (breast tomosynthesis) may find more breast cancers in women with dense breasts compared to 2D mammography .
Breast ultrasound and breast MRI (each combined with mammography) are being studied to learn whether they improve detection in women with dense breasts compared to mammography alone [111-112].
More research is needed to understand the benefits and harms of using these imaging tests (in addition to mammography) for women with dense breasts [113-114].
*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date.
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