Do You Have Dense Breasts? What It Means for Breast Cancer Risk and Screening
Key takeaways:
Dense breasts are breasts that have less fat and more fibrous tissue and glands. About 50% of women have dense breasts.
Dense breasts can make it harder for mammograms to detect cancer. They can also increase the risk for developing breast cancer.
Besides mammograms, there are other tests that can help detect breast cancer, including 3D mammograms, ultrasound, and MRI. There’s currently not enough evidence to recommend these tests for all women with dense breasts.
Table of contents
Many women learn that they have “dense breasts'' after their first mammogram. And it’s surprisingly common. Almost half of women 40 years and older have dense breasts, which can affect the reliability of a regular mammogram. So it’s helpful to understand what that means, and how that can influence your mammogram results and your risk factor for breast cancer.
A note on language: Sex and gender lie on a spectrum. We use the terms women and female in this article to refer to people assigned female at birth.
What does it mean if you have dense breast tissue?
To understand what it means to have dense breast tissue, it’s helpful to review the types of tissue in the breast. Breasts are made up of three elements:
Glandular tissues: These include lobules (small glands that produce milk) and ducts (the small tubes that carry milk).
Fibrous tissue: This helps give breasts their shape.
Fat: The amount of fat in breasts is what determines breast size.
If you have dense breast tissue, it means that you have a higher amount of glandular and fibrous tissue, and less fat.
But there’s a lot of misunderstanding about breast density, said Dr. Nicholas McAndrew, MD, MSCE, a breast cancer doctor at UCLA David Geffen School of Medicine in Los Angeles and a GoodRx contributor. “All women have some degree of breast density, and this can change over time as they get older. And it’s not something that can be felt.”
Breast density can only be measured by a mammogram. There are four categories of breast density:
Category A: Breasts are almost entirely fatty (10% of women).
Category B: There are scattered areas of fibrous and glandular breast tissue (40% of women)
Category C: The breasts have many areas of fibrous and glandular tissue (40% of women).
Category D: The breasts are extremely dense (10% of women).
Category C or D are considered dense breasts. Sometimes this will be documented in the mammogram report.
Why does breast density matter?
Breast density matters for two main reasons. When you have dense breasts:
Mammograms become less reliable because it’s harder to detect cancer.
Your chances of developing breast cancer at some point increase.
On a mammogram, fat will show up as transparent and black. The fibrous and glandular tissues look more white — the same color as early cancer. So it can be harder to detect cancer when more of the mammogram X-ray looks white from dense breasts.
Scientists don’t know why having dense breasts increases someone’s risk for breast cancer. It’s possible that the types of cells in dense breasts are more sensitive to the effects of hormones and growth factors, which can lead to increased cancer risk. Even though women with dense breasts are more likely to develop breast cancer, they’re not more likely to die of breast cancer than women with fatty breasts.
What causes dense breast tissue?
Most of the time, your genetics determine if you have dense breasts. Other factors that are linked with a dense breast tissue include:
Low body mass index (BMI)
Use of menopausal hormone therapy
Younger age
Not having children
How do doctors determine if you have dense breasts?
The only way to know if you have dense breasts is by looking at a mammogram. Breast density isn’t related to breast size or firmness. When looking at a mammogram, radiologists will look at the amount of fibroglandular tissue versus fatty tissue and categorize the level of breast density as described above.
The FDA says it’s important for every woman to know their breast density so that they can discuss an individual approach to breast cancer screening with their healthcare provider. In March 2023, the FDA ruled that all mammography facilities need to include information about breast density on the mammography report.
What are the other screening tests for breast cancer?
Mammograms aren’t the only way to screen for breast cancer. There are a few other
imaging tests for breast cancer screening.
3D mammogram
This is also called digital breast tomosynthesis. This type of mammogram uses extra images to create a 3D picture of the breasts. These images are better for cancer detection, including cancer in dense breast tissue. False positives are also less common with 3D mammograms compared with regular mammograms.
Ultrasound
For some people, an ultrasound can help detect breast cancer. It’s not the first choice screening test because it has increased false positive rates. This means it detects something as possible cancer, when it’s not. And this leads to unnecessary worry and testing, like biopsies. But it also means it can help detect cancer in dense breast tissue that may be harder to see on a regular mammogram.
MRI
MRI is very good at detecting cancers, even better than ultrasound. But like a breast ultrasound, it’s associated with a higher rate of false positives. And an MRI has other drawbacks, too. It’s not as widely available, and can be much more expensive — especially if insurance doesn’t provide coverage.
What is the best screening test if you have dense breast tissue?
Even though other tests are available for breast cancer screening, it doesn’t mean that they’re necessarily the best option if you have dense breast tissue.
The benefits of increased cancer detection needs to be weighed against the potential harms of extra testing. This includes unnecessary testing and worry from biopsies that otherwise wouldn’t have been needed.
In 2016, the U.S. Preventive Services Task Force conducted a large-scale review of all the research. The task force concluded there was not enough evidence to recommend these additional testing methods for women with dense breasts. This may change as more studies are done.
The American College of Obstetrics and Gynecologists (ACOG) also doesn’t recommend extra screenings if your only risk factor for breast cancer is dense breasts. This recommendation is based on the fact that women with dense breasts don’t have an increased risk of dying from breast cancer. And that mammograms are still considered an effective method of screening.
But if a mammogram shows an abnormal area in the breast, an ultrasound can help determine if it’s cancer. A mammogram and ultrasound — when used together — are better at detecting breast cancer than a mammogram alone.
Some experts think that 3D mammograms should still be offered to all women with dense breasts because of the increased accuracy. Additionally, the European Society for Breast Imaging (EUSOBI) recommends that women with extremely dense breasts (10% of the female population) should get a screening MRI every 2 to 4 years.
For now, many healthcare providers agree that breast cancer screening should be individualized. This means it should be based on an assessment of all the risk factors a person has, along with an understanding about the risks and benefits of various screening options.
“There is no one-size-fits-all approach to breast cancer screening,” McAndrew said.
“Individual risk may vary from person to person. An appropriate screening schedule for one person may be excessive for another,” he said. “We take into account things like family history of breast cancer, breast density, and the risks and benefits of more sensitive imaging tests to help women choose their ideal screening program.”
A note if you’re worried about dense breast tissue
If your only risk for breast cancer is having dense breasts, your overall risk for developing breast cancer is still quite low. Keep in mind that this is a common condition — half of all women have dense breasts.
Even so, it’s helpful to know what it means to have dense breast tissue. If you have a family history of breast cancer and have dense breasts, you and your healthcare provider may decide that you would benefit from a different kind of screening method instead of a regular mammogram.
The bottom line
Dense breast tissue is extremely common. Since dense breasts can make it harder for mammograms to detect cancer, it’s helpful to know whether your breasts are categorized as dense. But remember it’s only one factor, and the current guidelines in the U.S. don’t recommend different screening methods. If you know you have dense breasts, it’s worth discussing your personal risk factors with your healthcare provider to see if additional screening tests would be helpful.
Why trust our experts?
References
Guo, R., et al. (2018). Ultrasound imaging technologies for breast cancer detection and management: A review. Ultrasound in Medicine & Biology.
Lee, C. I., et al. (2017). Risk-based breast cancer screening: Implications of breast density. The Medical Clinics of North America.
Mann, R. M., et al. (2022). Breast cancer screening in women with extremely dense breasts recommendations of the European Society of Breast Imaging (EUSOBI). European Radiology.
Memorial Sloan Kettering Cancer Center. (n.d.). Anatomy of the breast.
National Cancer Institute. (2023). Dense breasts: Answers to commonly asked questions.
Siu, A. L. (2016). Screening for breast cancer: U.S. Preventive Services Task Force recommendation statement. Annals of Internal Medicine.
U.S. Food and Drug Administration. (2023). FDA updates mammography regulations to require reporting of breast density information and enhance facility oversight.
