What is fibroglandular density?

Fibroglandular density describes the type of tissue in your breast as seen on a mammogram. Your breasts consist of three types of tissue:

  • Fibrous connective tissue: Fibrous connective tissue is dense. It appears white on a mammogram. The tissue’s appearance makes it harder to detect cancerous tumors that also appear white. Having lots of this type of tissue is associated with high fibroglandular density (or dense breasts).
  • Glandular tissue: Glandular tissue is dense. Glandular tissue includes the milk glands and milk ducts in your breasts. This tissue appears white on a mammogram, making it harder to detect cancer. Having lots of this tissue is associated with high fibroglandular density.
  • Fatty tissue: Fatty tissue isn’t dense. Fatty tissue appears dark or see-through on a mammogram, making it easier to spot white areas indicating cancer. Having mainly fatty breast tissue is associated with low fibroglandular density.

Fibroglandular density compares the amount of fibrous connective tissue and glandular tissue to the amount of fatty tissue. It’s sometimes referred to as breast density.

Should I worry about fibroglandular density?

Fibroglandular density is important because dense breast tissue can make it harder for a radiologist to detect breast cancer on a mammogram. This is because both cancer and dense breast tissue appear white on the screen. This is referred to as masking — as in, dense breasts may “mask” cancer.

Don’t panic if you see dense breasts on your mammogram report. Based on your mammogram results and your breast cancer risk, your provider may suggest additional imaging tests to get a better look at your breasts.

What affects fibroglandular density?

It’s common to have dense breast tissue. 50% of women and people assigned female at birth (AFAB) fall into this category. Some factors that may make you more likely to have dense breasts include:

  • Age.
  • Medications that contain hormones.
  • Genetics.
  • Bodyweight.

Your provider can discuss your breast density with you and what it means for detecting cancer. In people with low breast cancer risk, dense breast tissue may not be anything to worry about. However, if you’re at higher risk for cancer, your provider may discuss your options for additional breast cancer screens.

What are the different types of fibroglandular density?

The density of your breast is divided into four categories, ranging from having very little dense tissue to extremely dense tissue. The four categories are:

RankClassificationDescriptionPrevalence
AMostly fatty tissue.Breast tissue is almost all fat.About 10% of women and people AFAB.
BScattered fibroglandular breast tissue.A mix of dense and fatty tissue, but mostly fatty.About 40% of women and people AFAB.
CHeterogeneously dense breast tissue.A mix of dense and fatty tissue, but mostly dense.About 40% of women and people AFAB.
DExtremely dense breast tissue.Breast tissue is almost all dense.About 10% of women and people AFAB.

What does scattered fibroglandular breast tissue mean?

Radiologists use a scale based on the Breast Imaging Reporting and Data System (BI-RADS) to classify your breast tissue as more fatty or more dense. BI-RADS ranks your fibroglandular density on a scale. Scattered fibroglandular density means you have a mix of dense and fatty tissue, but the majority is fatty. Heterogeneously dense breast tissue means you have a mix of dense and fatty tissue, but it’s mostly dense tissue. Together, these two categories make up 80% of the U.S. population.

Is scattered fibroglandular density cancer?

No. It’s a measurement of your breast tissue. Having scattered fibroglandular tissue means your mammogram shows some areas of density. Cancer and dense breast tissue appear white on a mammogram. Density is only related to breast cancer because a dense breast can make it more difficult for your healthcare provider to detect cancerous spots when they read your mammogram.

What are the common conditions and disorders associated with fibroglandular density?

Your fibroglandular density is associated with your breast cancer risk. There’s increasing evidence that a higher density means that you’re more at risk, including:

  • Mammogram technology doesn’t always detect cancer in dense breast tissue. Dense breast tissue can mask cancer on a mammogram. Mammograms can miss about 27% of cancer in dense breasts.
  • Dense breasts have a higher likelihood of cancer. The reasons are unclear, but you’re at a greater risk for developing breast cancer with dense breasts, compared to someone whose breasts are mainly fatty.

What tests measure fibroglandular density?

You’ll need a mammogram to show your fibroglandular density. A mammogram is a specialized X-ray that captures an image of the inside of your breasts.

Depending on what kind of breast tissue you have, more advanced imaging technologies may be helpful to see cancer developing.

  • 3D mammography (breast tomosynthesis): A low-dose X-ray (about 1.5 to 2 times more radiation than a standard 2D mammogram) captures several images of your breasts from multiple angles. These images are compiled to create a 3D image of your breasts. This allows better visualization in dense tissue because it decreases the phenomenon of overlapping breast tissue. This technology allows the radiologist to scroll through dense tissue, and can make abnormal areas more visible.
  • Breast ultrasound: Sound waves capture an image of your breast tissue and project it onto a screen.
  • Breast MRI: Magnets and radio waves record structures inside your breast and project those images onto a screen.
  • Molecular breast imaging (MBI): Your provider injects a radioactive tracer into a vein in your arm. The tracer is a liquid that flows through your bloodstream. A special camera records the tracer’s interaction with cancerous or noncancerous tissues in your body. These interactions show up on screen and look different depending on whether the tracer interacts with cancerous vs. noncancerous tissue.

Each type of imaging has its strengths and weaknesses. For instance, while MRIs and ultrasounds can identify cancers that mammography misses, they can also mistake noncancerous cells for cancerous ones (a false positive). Specialized tools, such as 3D mammography, can identify cancers that a traditional mammogram may miss, but it also uses slightly more radiation than a 2D mammogram. Extra radiation exposure can pose risks if you’re at high risk of developing cancer. Also, the availability of these technologies and their affordability based on insurance coverage varies.

Talk to your provider about which screening options they’d recommend based on your risk of developing breast cancer. It’s important to remember that screening mammography remains the gold standard for early detection of breast cancer. The other technologies described above, including breast ultrasound and breast MRI, supplement screening mammography. They aren’t a replacement for routine breast cancer screening.

What questions should I ask my healthcare provider?

Ask your provider about your fibroglandular density. Once you learn how dense your breasts are, ask about what your breast density means for your health. Questions to ask include:

  • How likely am I to develop breast cancer?
  • Are my breasts dense?
  • How does my breast density affect the results of a mammogram?
  • What types of imaging are best for detecting cancer?
  • What types of imaging do you recommend for screening for breast cancer?
  • Do I need to consider any type of supplemental screening?
  • How often should this imaging be done?

A note from Cleveland Clinic

Hearing your provider talk about fibroglandular density can be scary when you’re worried about your breast cancer risk. But you shouldn’t be concerned. Your breasts are made up of tissue that may or may not pose challenges for cancer screenings. Having dense breasts, or high fibroglandular density, means you may benefit from additional imaging to make up for some of the limitations of mammography.

Last reviewed by a Cleveland Clinic medical professional on 01/12/2023.

References

  • American Cancer Society. Breast Density and Your Mammogram Report. (https://www.cancer.org/cancer/breast-cancer/screening-tests-and-early-detection/mammograms/breast-density-and-your-mammogram-report.html) Accessed 1/12/2023.
  • Centers for Disease Control and Prevention. What Does It Mean to Have Dense Breasts? (https://www.cdc.gov/cancer/breast/basic_info/dense-breasts.htm) Accessed 1/12/2023.
  • Comstock CE, Gatsonis C, Newstead GM, et al. Comparison of abbreviated breast MRI vs digital breast tomosynthesis for breast cancer detection among women with dense breasts undergoing screening. (https://pubmed.ncbi.nlm.nih.gov/32096852) JAMA. 2020;323(8):746-756. Accessed 1/12/2023.
  • Kyanko KA, Hoag J, Busch SH, et al. Dense breast notification laws, education, and women's awareness and knowledge of breast density: a nationally representative survey. (https://pubmed.ncbi.nlm.nih.gov/31916210/) J Gen Intern Med. 2020;35(7):1940-1945. Accessed 1/12/2023.
  • Nazari SS, Mukherjee P. An overview of mammographic density and its association with breast cancer. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5906528) Breast Cancer. 2018;25(3):259-267. Accessed 1/12/2023.

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