We explain what exactly dense breasts are, how it impacts breast screening, and more.
If you’ve ever had a mammogram, you’ve probably at least heard of dense breasts. Nearly half of women over 40 have them — including Katie. Those that do may need a special type of breast cancer screening and have an increased risk of developing breast cancer.
But what are dense breasts exactly? And how can you tell if you have them? We’re here to answer all your questions and more.
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 recent 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 breast sees over a lifetime with some areas of the breast being more glandular, others being fattier.”
Thanks to a new 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.
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, tells KCM. That’s because fatty tissue appears dark on a mammogram, while fibrous and glandular tissue looks white, like tumors do.
“It can make finding cancer a bit like finding a polar bear in a snowstorm,” she says.
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, says Natasha Robinette, M.D., an oncology radiologist at the Karmanos Cancer Institute in Detroit. And new tools to help improve detection in dense breasts are still being developed, like SoftVue, a new 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.
Why do dense breasts increase the risk of breast cancer?
Scientists have a couple 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 says.
