We explain what exactly dense breasts are, how it impacts breast screening, and more.
Nearly half of women over 40 have dense breasts — including Katie. Those who do may need a special type of breast cancer screening and have an increased risk of developing breast cancer.
But many women may not even know they have them or why it’s significant. A friend of Katie’s learned she did after receiving a routine mammogram, which 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 yourself if you have them. Here’s a breakdown of what you need to know.
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 high amounts of fibrous and glandular tissue relative to fatty tissue.
As we age, the composition of our breasts usually changes, Lisa Newman, M.D., the head of breast surgery at New York Presbyterian Weill-Cornell, 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 have four ranges to describe breast density. Level A is a breast that’s almost entirely fatty tissue. Only about 1 in 10 women fall into this category, according to the Centers for Disease Control and Prevention. Level B, where there are a few areas of dense tissue scattered through the breast, accounts for about 40 percent of women. Another 40 percent of women have breasts that are evenly dense throughout — categorized as Level C, while 10 percent of women have breasts that are extremely dense and classified as Level D.
Women in these last two levels have dense breasts.
How can you tell if you have dense breasts?
You won’t be able to judge a breast’s level of density based on its feel or appearance. The only way to measure it for sure is to get a mammogram, according to the National Institute of Health.
“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 2023 Food and Drug Administration ruling, mammogram providers must tell patients whether their breasts are dense (Levels C and D) or not dense (Levels A and B). Previously, only doctors in some states were required to notify women.
Still, few are told what their diagnosis means or what they should do next. That’s changing: On September 10, the Food and Drug Administration (FDA) issued a final rule requiring breast density to be included in mammography reports. This amendment to the Mammography Quality Standards Act (MQSA) states that all mammogram facilities should include information about breast density in all patient mammography reports and results letters. Thanks to this update, patients with dense breasts will get more guidance about their cancer risks.
Over 35 states and the District of Columbia already require some assessment of breast density. The FDA’s new rules are designed to simplify the medical jargon so it’s understandable to anyone, including those with low literacy, and give clearer guidance. According to Cancer.org, if your breast tissue is dense, the report will say, “Breast tissue can be either dense or not dense. Dense tissue makes it harder to find breast cancer on a mammogram and also raises the risk of developing breast cancer. Your breast tissue is dense. In some people with dense tissue, other imaging tests in addition to a mammogram may help find cancers. Talk to your healthcare provider about breast density, risks for breast cancer, and your individual situation.”
Mammogram reports sent to healthcare providers must also now include an overall assessment of breast density using the four categories (A through D).
How does having dense breasts affect cancer screening?
Dense breasts are more difficult to screen for cancer using a traditional mammogram, Lillie Shockney, R.N., 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 an additional screening. A breast tomosynthesis — also called 3-D mammography — is one option, Shockney says. This tool allows clinicians to adjust the contrast of an image, which helps them better distinguish between the white of a harmless breast lobule and that of a potentially dangerous mass.
Breast ultrasounds, like the one Katie received, are also sometimes used, said Natasha Robinette, M.D., an oncology radiologist at the Karmanos Cancer Institute in Detroit. New tools to help improve detection in dense breasts are still being developed, like SoftVue, a newer type of breast ultrasound created by researchers at Karmanos. This tool, which was only recently approved by the FDA, works much faster than an automated breast ultrasound and, when used with a traditional mammogram, increases detection by about 20 percent.
However, these additional scans may not be covered by insurance. The U.S. Preventive Services Task Force — a body of physicians and other healthcare providers that insurers look to for guidance when writing their policies — released their updated guidance on breast cancer screenings, which lowered the recommended age to 40, but did not endorse supplemental exams for women with dense breasts.
Why do dense breasts increase the risk of breast cancer?
Scientists have a couple of theories. One link that’s being studied is the connection between female sex hormones and dense breasts. People with dense breasts tend to have high levels of these hormones, which has been shown to be a risk factor for breast cancer. Another theory, Dr. Robinette says, is that since there’s more glandular tissue in dense breasts, there are also just more glandular cells, which may have the potential to become cancerous.
“It’s really not known, the data just shows that women with dense breasts are at an increased risk,” Dr. Robinette said.
