What you need to know about breast density

If you recently had a mammogram, you may have noticed that the mammography report you received afterward includes information on whether you have dense breasts. Breast density is a measurement that describes the amount of fat tissue versus fibrous and glandular tissue in the breasts. Almost half of all women age 40 and older are found to have dense breasts.

Radiologists have been measuring breast density for some time. Still, breast density and its impact on breast cancer risk isn’t always clearly communicated — and sometimes, it isn’t communicated at all. If breast density has never been explained to you, you’re not alone.

Until recently, individual states governed whether breast density information was shared with patients. However, the FDA has mandated that by September 2024, all mammogram reports sent to patients must include their breast density information. Unfortunately, the FDA requirement does not mean that providers will clearly and effectively explain what your results mean.

Learning your breast density status can raise questions about your breast health and breast cancer screening, especially if your doctors haven’t discussed it with you before. On this page, we’ll answer those questions and more.

What is dense breast tissue?

Breasts are made up of different kinds of structures and tissues, including:

• Lobules — small glands that produce breast milk
• Ducts that carry breast milk to the nipple
• Fibrous tissue that provides structure for the lobules and ducts
• Fatty tissue

Together, the lobules (glands), ducts, and fibrous tissue are called fibroglandular tissue. The more fibroglandular tissue you have, the denser your breasts are.

Dense breast tissue can only be seen on imaging tests, which is why women only find out about their breast density after mammography screening. You can’t feel whether you have dense tissue by doing a breast self-exam, and breast density is not related to how firm breasts feel or what size they are.

Breast density matters because dense breast tissue makes it more challenging for radiologists to see cancer on a mammogram. This is because on a mammogram, while fatty tissue appears as black, fibroglandular tissue appears as white — and breast cancer also appears as white. If there’s a lot of fibroglandular tissue, it’s harder to see cancer. In addition, research shows that women with dense breasts have a higher risk of breast cancer, though doctors do not currently know why. One theory is that dense breast tissue contains more cells that could potentially become abnormal.

What affects breast density?

Breast density varies from person to person. It is often inherited, so if you know someone in your family has dense breasts, it’s possible that you do, too. Dense breasts are more common in younger women and women with a lower body mass index (BMI), while less dense breasts are more common in older women and in women who have given birth. People taking hormone replacement therapy (HRT) for menopause are also more likely to have dense breasts. It’s important to know that if you are at risk for or have a history of breast cancer, HRT is not recommended.

For many women, breast density naturally decreases with age. However, some women may see no change in density over time.

Significant weight changes can also impact how dense your breasts appear on a mammogram. When you gain a significant amount of weight, the fat tissue in your breasts increases, and your breasts can appear to be less dense. Similarly, if you lose a lot of weight, your breast tissue can appear denser. However, even if you have significant weight changes, the actual amount of dense tissue does not change.

You may see information suggesting that certain foods and supplements can increase or decrease the density of your breasts. Researchers are looking at whether there is an association between diet and breast density, but results are mixed, and more research is needed. Talk with your healthcare team about a nutrition plan that’s right for your individual situation and risk of breast cancer.

How is breast density defined?

When a radiologist looks at your mammogram, they’ll assess how much fibroglandular tissue is present compared to how much fatty tissue is present. Then, they’ll assign it to one of four categories, or density levels.

A. Fatty. The breast is mostly comprised of fatty tissue, with little or no fibroglandular tissue.
B. Scattered. There are some areas of fibroglandular tissue within the breast, but most of the breast is fatty tissue.
C. Heterogeneously dense. The breast has some areas of fatty tissue, but most of the breast is comprised of fibroglandular tissue.
D. Extremely dense. The breast has little to no fatty tissue.

Of the categories above, only C and D are considered to be dense breasts.

Breast density and breast cancer risk

Research shows that people with dense breasts are more likely to develop breast cancer than people whose breast tissue is mostly fatty tissue. But right now, it is not clear why. What we do know is that the denser the breast tissue, the higher the risk for cancer, and the harder it is for mammograms to detect it.

Because mammograms are less sensitive for people with high breast density, some doctors will recommend additional kinds of imaging tests to look for cancer if you have dense breasts.

Different professional medical organizations have different guidelines about whether women with dense breasts should have supplemental screenings. Right now, the US Preventive Services Task Force (USPSTF) says it is not yet clear that there’s value in supplemental screenings because they often lead to false-positive results. A false-positive means the test shows you have signs of cancer when you actually do not. According to the USPSTF, this can lead to other tests, such as biopsies, that they say are unnecessary if the results turn out to be benign.

Still, the National Comprehensive Cancer Network (NCCN) recommends that women with dense breasts have a discussion with their doctors about the potential benefits and risks of additional types of screening, such as breast MRI and ultrasound.

And if you have any other risk factors for breast cancer — such as a personal history of breast cancer, a strong family history of breast cancer, or other high-risk factors — let your doctor know. These can also be reasons that your doctor may recommend supplemental screenings.

Breast cancer screening for people with dense breast tissue

Supplemental screening tests doctors may recommend for dense breasts include:

• 3D mammography, or digital breast tomosynthesis. This type of mammogram is shown to find breast cancers that typical 2D mammograms do not.
• MRI. MRIs can help find cancers that typical mammograms do not, but may lead to false-positive results.
• Ultrasound. Like MRIs, ultrasounds are known to find cancers that mammograms miss, but they also may lead to false-positives.
• Contrast-enhanced mammogram. This is a standard 3D mammogram with IV contrast to help highlight abnormalities.

Comparing the pros and cons of supplemental screening tests

3D mammogram, or digital breast tomosynthesis. This type of mammogram is shown to find breast cancers that typical 2D mammograms do not.
Pros:

• Estimated to detect about 1 additional cancer per 1,000 women
• Done at the same time as a standard mammogram
• Reduces the need for being called back for additional testing of areas of concern that aren’t cancer
• Helpful in evaluating dense breast tissue

Cons:

• Exposes you to additional radiation, though levels are still very low
• Availability is becoming more common

Breast MRI. MRIs can help find cancers that typical mammograms do not, but may lead to false-positive results.
Pros:

• Estimated to detect about 14 additional cancers per 1,000 women
• No additional radiation exposure
• Widely available

Cons:

• Likely to find areas of concern that aren’t cancer, but that require additional imaging or a biopsy
• Requires injection of contrast material
• Expensive test that might not be covered by insurance unless you have a very high risk of cancer

Breast ultrasound. Like MRIs, ultrasounds are known to find cancers that mammograms miss, but they may also lead to false positives.
Pros:

• Estimated to detect an additional 2-4 cancers per 1,000 women
• No additional radiation exposure
• Widely available

Cons:

• Likely to find areas of concern that aren’t cancer, but that require additional imaging or a biopsy
• Quality of exam dependent on experience of person doing the test

Used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.

What do I do if I have dense breasts?

In March 2023, the FDA announced that all U.S. mammography centers must inform women whether their breasts are “dense” or “not dense” by September of 2024. This information may be communicated in a letter or a report you receive after having a mammogram. Many states already have this requirement.

If you’ve been notified that you have dense breasts, your first step is to talk to your doctor about what the result means for you. Your family and medical history may play a role in whether your doctor recommends supplemental screenings to look for cancer.

Your annual screening mammogram is covered by insurance under the federal 2010 Affordable Care Act. But if you have dense breasts, supplemental screening tests may not be covered by your insurance. This is because individual state legislatures can decide whether insurance companies should cover supplemental screenings for dense breasts. So, where you live can impact whether your insurance will cover additional screening.

DenseBreast-Info.org offers a legislative map to help you determine if your home state offers coverage. You can also call your insurance provider to learn whether dense breast supplemental screening, such as 3D mammogram, ultrasound, or MRI, is covered. If you have difficulty getting coverage for screening, let your healthcare team know. They may be able to help.

Questions to ask your healthcare team about breast density

• Do I have dense breasts? If so, what category of density is it?
• (If you have dense breasts) What is my individual risk of developing breast cancer, now that we know I have dense breasts?
• What additional screening do you recommend, if any?
• If additional screening is not covered by my insurance, is there anything you can do, or are there any programs that can help?
• Can I do anything to decrease my breast density?
• What can I do to lower my risk of breast cancer?
• My results said I do not have dense breasts. Can that change over time?

Know that you are not alone

Having dense breast tissue is common. Half of all women who get mammograms find out they have dense breasts — 40 percent in the heterogeneously dense category, and 10 percent in the extremely dense category. As research continues, we will all learn more about what we can do to manage the cancer risks related to breast density.

Some people are more likely than others to be diagnosed with breast cancer, and that can include people with dense breast tissue. If you’ve learned that you have a high risk of developing breast cancer, but have not been diagnosed, visit our At high risk for breast cancer resource page.