Breast Density: What it is and What it Means to You

Main Line Health is committed to helping you understand what is currently known about breast density and its implications for breast cancer screening, so you will be better prepared to work with your doctor to protect your breast health.

What are "dense breasts?"

To understand what “dense breasts” means, it helps to know a bit about breast tissue. breasts are made up of a combination of three types of tissue: fatty tissue, fibrous tissue (also called connective tissue), and glandular tissue. The fatty and fibrous tissues give breasts their shape, and the glandular tissue produces milk.

Breasts vary in how much fatty, fibrous, and glandular tissue they contain. When there is a lot of fibrous and glandular tissue but not much fatty tissue, breasts are described as being “dense.” Thus, dense breasts are not abnormal; they are simply one end of the normal spectrum of breast tissue. While it is not clear why some women have dense breasts and others do not, if your mother has or had dense breasts you are more likely to also have dense breasts.

How do I know if I have dense breasts?

Breast density has nothing to do with how firm your breasts are or how they look. It is not something you can see or feel from the outside. Breast density can only be determined by a radiologist who is experienced at reading mammograms and judging the amount of fatty versus fibrous or glandular tissue present in a breast.

There are four categories of breast density, shown below as they appear on mammograms and with the terms radiologists use to describe them.

If your mammogram shows that you have category C or D breast density, your mammography report will state that you have “dense breasts.” More than 40 percent of women have category C or D breast density. Breast density may decrease somewhat with age or change over time, which may result in different density reports from one mammogram to another.

Why is breast density important?

Breast health specialists have long recognized that dense breast tissue can make it harder to spot abnormalities on mammograms. Dense breast tissue appears white on a mammogram and, thus, can potentially hide lumps (benign or cancerous), which also appear white. Fatty breast tissue, on the other hand, appears dark on a mammogram and, thus, allows a radiologist to be more confident in reporting that there is no abnormality. The potential for mammograms to be less accurate in dense breasts is one reason laws are now in place to inform women about their breast density.

Studies also link breast density with a higher risk for getting breast cancer, although it is not clear what about breast density raises a woman’s risk. The risk for breast cancer is twice as high in women with category D breast density as it is in women with breast density between categories B and C; women with category C breast density have only a slightly increased risk. Studies show that women with dense breasts who do develop breast cancer are not at greater risk for worse outcomes.

Do I still need mammograms if I have dense breasts?

Yes. Even if you have category D breast density and you and your doctor decide you should have additional screening tests for breast cancer, you should continue to have regular mammograms. To date, mammography is the only screening test that has been shown in large studies to lower the risk of death from breast cancer.

These studies included women with all types of breast density, including category D. In addition, mammography is the only test that can reliably spot calcifications in the breast. These are often the first sign of a hidden cancer.

What are the "screening options" mentioned in my mammography report?

Researchers are actively studying options to mammography alone to see if there is an even better approach to screening for breast cancer in women with dense breasts. A “better” screening approach should offer greater accuracy in detecting cancer but not at the expense of more biopsies (surgeries) for “false alarms” that turn out not to be cancer.

The most-studied screening tests for breast cancer are:

  • 3D mammography (Breast tomosynthesis) – Recent studies show that breast tomosynthesis may improve detection of cancers in women with dense breasts, without the risk of increased false alarms. This new form of mammography is performed with machines that take standard digital mammograms 2D images) and then combine them into 3D images.
  • Breast MRI – Breast MRI has been shown to help find cancers that are not visible on a mammogram, but at the risk of more false alarms.
  • Breast ultrasound – Breast ultrasound also has been shown to help find cancers not visible on a mammogram, but not as reliably as breast MRI and also with the risk of false alarms.

What should I do if I have dense breasts?

You may not need to do anything other than what you are already doing. However, if you learn you have dense breasts, talk with your primary care doctor or gynecologist about your overall risk for breast cancer. Breast health specialists use several different tools to estimate a person’s risk based on the presence or absence of certain known risk factors for breast cancer. If a risk assessment indicates you are at high risk for breast cancer, you may benefit from having a breast MRI as well as a mammogram each year.

Talking to your doctor

Here are some questions to start a conversation with your doctor about breast density:

  • What does my mammography report say about my breast density? Are there any details from the radiologist I need to understand?
  • What is my risk for breast cancer? Can we do a risk assessment together?
  • Should I have other screening tests for breast cancer in addition to mammography?
  • If I should have other tests, which test is recommended and why?
  • Are there any downsides to the additional test?
  • Should I have screening more often than once a year?

Breast imaging services

Main Line Health provides comprehensive, state-of-the-art breast imaging services at each of its four hospital-based Breast Centers, allowing you to choose the location most convenient for you.

Each Center offers 3D Mammography (breast tomosynthesis) as well as breast MRI and breast ultrasound. Find a breast center near you.

To schedule a mammography appointment at Main Line Health, call 484.580.1800