Do You Have Dense Breasts? Here’s How To Find Out — And What To Know About the Cancer Risks

About half of women who get mammograms have dense breasts — including Katie. Those who do may need additional breast cancer screening and have an increased risk of developing breast cancer.

But many women may not even know they have dense breasts or why it matters. A friend of Katie's learned she did after a routine mammogram came back clean. After hearing about Katie's experience (and reading Wake-Up Call), she requested an additional screening and was diagnosed with breast cancer. This is just one example of why it's so important that all women have an understanding of what dense breasts are and how to protect themselves if they have them.

Here's what qualifies as "dense" and how screenings differ.

What are dense breasts?

The breast is made up of three types of tissue: glandular, fibrous, and fatty tissue. Glandular tissue is the part of the breast that produces milk and delivers it to the nipple. Fibrous tissue is made of the same stuff as our ligaments and scar tissue and holds the breast in place, while fatty tissue gives the breast its size and shape. Dense breasts have more fibrous and glandular tissue relative to fatty tissue.

As we age, the composition of our breasts usually changes, Lisa Newman, MD, the head of breast surgery at NewYork-Presbyterian/Weill Cornell Medical Center, told Katie during a live event on breast cancer supported by Hologic. “In general, the glandular elements of the breast tend to be replaced by more fatty tissue as we get older,” meaning that over time, a woman's breasts may become less dense.

So younger women — as well as those undergoing hormone replacement therapy — are more likely to have dense breasts, Dr. Newman said.

Clinicians use four categories to describe breast density. Category A is a breast that’s almost entirely fatty tissue. About 1 in 10 women fall into this category, according to the National Cancer Institute. Category B, where there are scattered areas of dense fibroglandular tissue throughout the breast, accounts for about 40 percent of women.

Another 40 percent of women have heterogeneously dense breasts — categorized as Category C — while about 10 percent of women have extremely dense breasts and are classified as Category D.

Women in these last two categories are considered to have dense breasts.

How can you tell if you have dense breasts?

You can’t judge a breast’s density by feel or appearance. Only a radiologist looking at a mammogram can determine whether a woman has dense breasts, according to the National Cancer Institute.

“The quantification of breast density is something that is determined by the breast radiologist,” Dr. Newman told Katie. “Women very commonly will have fibrocystic densities that you can feel on clinical breast examination, but that is different from breast density. Every woman has some degree of lumpy bumpiness in the breast, and that's simply a sequela of all the hormonal cycles that our breasts see over a lifetime, with some areas of the breast being more glandular, others being fattier.”

Thanks to a Food and Drug Administration rule that took effect on September 10, 2024, mammography facilities subject to federal standards must tell patients whether their breasts are dense (Categories C and D) or not dense (Categories A and B). Previously, breast density notification requirements varied by state.

The FDA rules are designed to give patients clearer information about what their breast density means. If your breast tissue is dense, your results must explain that dense tissue can make it harder to find breast cancer on a mammogram and also raises the risk of developing breast cancer. The notification also notes that in some people with dense tissue, other imaging tests in addition to a mammogram may help find cancers, and advises patients to talk to their healthcare provider about breast density, breast cancer risk, and their individual situation.

Mammogram reports sent to healthcare providers must also include an overall assessment of breast density using the four categories (A through D).

@katiecouric

This one goes out to all my fellow dense breast girls 💕

♬ original sound - Katie Couric

How does having dense breasts affect cancer screening?

Dense breasts are more difficult to screen for cancer using a traditional mammogram, Lillie Shockney, RN, a professor of surgery at Johns Hopkins Medicine, told Katie Couric Media. That’s because fatty tissue appears dark on a mammogram, while fibrous and glandular tissue looks white, like tumors.

“It can make finding cancer a bit like finding a polar bear in a snowstorm,” she said.

Because of this, if you have dense breasts, a doctor may recommend additional screening depending on your individual breast cancer risk. A breast tomosynthesis — also called 3-D mammography — is one option, Shockney says. This technology takes multiple X-ray images of the breast from different angles, which are reconstructed into a three-dimensional image.

Do you need additional screening if you have dense breasts?

Breast ultrasounds, like the one Katie received, and breast MRI are also sometimes used as supplemental screening for women with dense breasts. However, having dense breasts doesn’t automatically mean you need additional imaging. The National Cancer Institute notes that there still isn’t enough evidence to recommend for or against additional imaging such as ultrasound or MRI for all women with dense breasts. Your healthcare provider can help determine whether supplemental screening makes sense based on your breast density and other breast cancer risk factors.

Additional scans may not always be covered by insurance, and coverage can vary depending on your health plan, state, individual risk, and the type of imaging. The U.S. Preventive Services Task Force recommends that women ages 40 to 74 get a mammogram every other year, but has concluded that there isn’t yet enough evidence to recommend for or against supplemental ultrasound or MRI for women with dense breasts after an otherwise negative mammogram.

Why do dense breasts increase the risk of breast cancer?

Scientists don’t yet fully understand why dense breast tissue increases breast cancer risk. Researchers are studying several possible explanations, including the biological characteristics of dense breast tissue and the fact that dense breasts contain more glandular and fibrous tissue and less fatty tissue.

“It’s really not known, the data just shows that women with dense breasts are at an increased risk,” Dr. Robinette said.