This World Dense Breast Day, learn why dense breasts raise cancer risk and complicate screening—and how research is closing the gap.
Key Takeaways
- Nearly half of women over 40 have dense breasts.
- Women with dense breasts have a higher risk of breast cancer.
- Dense breast tissue can be hard to read on a mammogram..
- BCRF researchers are studying new screening methods for women with dense breasts.
Dense breasts are a growing focus of breast cancer research. Around half of women over 40 have them, and they are associated with a higher risk of developing breast cancer. But what, exactly, are dense breasts?
Breasts contain three types of tissue. Fibrous (also called connective) tissue keeps the breast in place. Glandular tissue, which includes lobules and ducts, produces and transports breastmilk. Together, these two tissues are called fibroglandular tissue. The third type is fatty tissue, which surrounds the other tissues and helps create the size and shape of the breast.
Having dense breasts means you have more fibroglandular tissue than fatty tissue—and it’s completely normal.
Still, high breast density matters because it can make breast cancer harder to detect and more likely to develop. It’s also more common in younger women, as well as Asian and Black women—groups that, in different ways, already face greater risks and/or disparities in breast cancer outcomes. That’s why BCRF researchers continue to study breast density and new screening tools to give all women the best chance at early detection.
As we mark World Dense Breast Day on September 24, here are four important things to know about dense breasts.
1. Dense breasts are linked with increased cancer risk.
Dense breasts are not rare—in fact, they’re the reality for nearly half of all women over age 40. Breast density can range from entirely fatty to extremely dense. Breast density is typically greater in women under 40 and tends to lessen with age. On a mammography report, radiologists classify the density of a woman’s breast into one of four categories:
- A: entirely or almost entirely fatty, which occurs in about 10 percent of women
- B: scattered areas of fibroglandular density (or a few areas of dense tissue through the breast), which occurs in about 40 percent of women
- C: heterogeneously dense (considered “dense breasts”), which occurs in about 40 percent of women
- D: extremely dense, which occurs in about 10 percent of women
Women with dense breasts face a 15 to 20 percent increased risk of developing breast cancer compared to the national average, according to the American Cancer Society (ACS). Scientists are still working to uncover why that is. Since breast cancer often develops in glandular tissue, having higher amounts of it may simply create more opportunities for abnormal cells to grow and multiply.
It’s worth noting that breast cancer patients with dense breasts do not face a higher risk of death than individuals with non-dense breasts, per the Centers for Disease Control and Prevention (CDC).
2. Dense breast tissue makes mammograms harder to read.
Dense breast tissue can also make it more difficult for radiologists to spot cancer on a standard mammogram (also called a 2D mammogram). While fatty tissue appears almost black on a mammogram, dense glandular and fibrous tissue looks light gray or white, like breast masses do. That overlap can hide tumors in the image and increase the risk that a potentially cancerous growth goes undetected. This also contributes to higher rates of late breast cancer diagnoses among women with extremely dense breasts, according to a 2022 report in Springer.
While standard mammograms aren’t perfect, they still can show most breast cancers—including those in dense breasts. And as of 2024, the U.S. Food & Drug Administration (FDA) requires all mammogram facilities in the U.S. to notify patients of their breast density in their report. That means you’ll have an updated status on your breast density after every mammogram and you can work with your doctor to decide whether additional screening measures might be right for you.
3. Cancer screening in dense breasts is improving—but still imperfect.
Women with dense breasts can access more advanced screening tools to increase the likelihood of detecting cancer. More than 90 percent of all screening facilities in the U.S. now offer 3D mammograms, according to FDA data from March 2025. Also known as digital breast tomosynthesis, a 3D mammogram uses low-dose X-rays to take multiple images of the breast in an arc-like pattern. Software then reconstructs those images into thin “slices,” which radiologists can review one by one to check for abnormal growths.
Research has found that 3D mammograms, which are already part of standard breast cancer screening for many women, improve detection rates in women with heterogeneously dense breasts. For women with extremely dense breasts, however, the benefits are less clear—3D imaging can still miss cancers within very dense tissue.
Experts have yet to determine which secondary cancer screening tests, if any, should be standard for women with dense breasts. Healthcare professionals may recommend whole breast ultrasounds, which use sound waves to help differentiate between likely benign fluid-filled masses and potentially cancerous solid masses. Another common option is breast magnetic resonance imaging (MRI), which uses magnets and radio waves to form an image of the breast. This type of screening can help a radiologist detect concerning lesions hidden within breast tissue more accurately than mammograms or ultrasounds, but it can be cost prohibitive.
These tools are more sensitive, which means they can highlight cancers that a mammogram might miss. The flip side is that they can also flag areas that aren’t cancer at all (false positives), leading to extra tests, biopsies and worry for patients.
4. Researchers are studying new cancer screening tools for dense breasts.
As women with dense breasts face both a higher risk of cancer and less precise screening, BCRF researchers are studying new tools for earlier and more accurate detection. They’ve already found that abbreviated breast MRIs can detect invasive breast cancer more effectively than 3D mammography in women with dense breasts. They’ve also discovered that Molecular Breast Imaging (MBI) can help doctors see rapidly dividing cells that may be cancerous.
BCRF researchers are also evaluating if contrast-enhanced mammography (CEM) is more effective than 3D mammography at detecting cancer in women with dense breasts. The results of these trials could open the door to new screening standards for women with dense breasts.
Research into dense breasts can help inform the next generation of breast cancer screening and ensure that women with dense breasts get clearer answers about their health—ultimately bringing us closer to our goal of zero deaths from breast cancer.
