Breast density

Breast density is not about how your breasts look or feel. You can only find out if you have dense breast tissue through mammography. Having dense breasts does not mean that you will get breast cancer – but it does mean that your risk is increased.

There are different types of tissue in the breasts.

Fatty tissue is made up of fat. It helps give the breasts their shape and size.

Glandular tissue is made up of ducts and the milk glands (called lobules).

Fibrous tissue is the supportive tissue of the breast. It holds the glandular tissues in place. Along with fatty tissue, it gives the breasts their shape and size. It’s also called connective tissue.

Glandular tissue and fibrous tissue are thicker (denser) than fatty tissue. Breast density is the amount of dense tissue compared to non-dense tissue. You have dense breasts if you have more glandular tissue and fibrous tissue than fatty tissue in your breasts.

Find out more about the breasts.

Having dense breasts is common and it’s not abnormal. You might just have more dense tissue than someone else. Or you might have less. It is common in younger women and is also found in older women who take hormone replacement therapy (HRT).

Breasts become less dense with age for most women. In some women there’s little change in their breast density as they grow older. Breast density is often inherited. Other factors that can increase or decrease breast density include:

• age
• having children
• tamoxifen use
• HRT use after menopause
• having a low body mass index
• drinking alcohol

Breast density can only be seen on a mammogram. It can’t be found by having a healthcare professional examine your breasts or by examining your breasts yourself. Breast density is not related to the size, look or feel of your breasts.

After you have had a mammogram, the pictures of your breasts are looked at by a radiologist. Fatty tissue looks dark on a mammogram, and fibrous and glandular tissues look white.

A system called BI-RADS is used to classify breast density into 4 categories from A to D. These categories describe the amount of fatty or dense tissues found in your breasts. The amount of breast density increases from A to D.

BI-RADS A: The breast is mostly fatty tissue. About 10% of women are in this category.

BI-RADS B: The breast has a few areas of dense fibrous and glandular tissues. About 40% of women are in this category.

BI-RADS C: The breast is an almost equal mix of fatty and dense tissue. About 40% of women are in this category.

BI-RADS D: The breast is almost entirely dense tissue. About 10% of women are in this category.

Dense breast tissue makes it harder to find cancer in the breast. Normal dense breast tissue looks white on a mammogram, and so do tumours. So dense tissue can hide tumours. This means mammograms may not be as accurate in finding tumours in women with dense breasts.

Research has also shown that breast cancer risk increases with the amount of dense breast tissue a woman has. Breast density is a small part of your overall risk – having dense breasts does not mean that you will get breast cancer. But it does mean that your risk is increased.

Find out more about risk factors for breast cancer.

If you have dense breasts, research has also shown that you are no more likely to die from breast cancer than someone who does not have dense breasts.