How Do Dense Breasts Influence Breast Cancer Risk? Katie Couric's Diagnosis, Explained

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Katie Couric is seated and speaking to her interviewer

Katie Couric is seated and speaking to her interviewer

Photo: Mike Windle/Getty Images

Katie Couric announced Wednesday that she was diagnosed with breast cancer earlier this year, and had just finished her final round of radiation for the disease this week.

“Every two minutes, a woman is diagnosed with breast cancer in the United States,” Couric, 65, wrote on Instagram. “On June 21st, I became one of them.”

Couric, whose first husband died from colon cancer in 1998, has long been a proponent of cancer research and screenings—the former Today co-host even broadcasted her own colonoscopy to raise awareness for the disease.

Now, with her own cancer diagnosis, Couric wrote that she wanted to share her experience to encourage others to stay on top of their recommended cancer screenings—particularly if they have certain risk factors.

"I wanted to share my personal story with you all and encourage you to get screened and understand that you may fall into a category of women who needs more than a mammogram," she wrote.

That category, Couric wrote in a blog post, are people who have dense breasts, which includes herself. "Forty-five percent of women in this country (yes, nearly half) have dense breasts," Couric wrote, "which can make it difficult for mammograms alone to detect abnormalities.

Here's what to know about dense breasts, how they can influence cancer risk, and the barriers that still exist in breast cancer diagnoses.

What Does it Mean to Have Dense Breasts?

You may have heard that breasts are made up of fat, but that's not entirely true.

Breasts consist of three different kinds of tissue: fibrous tissue, which holds breast tissue in place; glandular tissue, which makes and delivers milk; and fatty tissue, which gives breasts their size and shape. Sometimes, fibrous tissue and glandular tissue are grouped together and called fibroglandular tissue.

“Any woman’s breast is composed of what we call fibroglandular tissue, or just tissue, and there’s a big component that is fat,” Jessica Leung, MD, professor and deputy chair in the department of breast imaging at the University of Texas MD Anderson Cancer Center, told Health.

Essentially, someone with dense breasts has a higher percentage of fibroglandular tissue than breast fat—something that is entirely out of their control.

"It's just the makeup of a patient. A little bit is related to your overall body mass index, but most of it is due to age or genetic reasons—different women are formed differently, that's all," Dr. Leung said. "There's nothing wrong with dense breast tissue."

On a more granular level, mammography reports can inform patients and their healthcare providers about their breast density, which can fall into one of four categories:

  • Breasts that are almost entirely fatty (about 10% of women)
  • Scattered areas of dense tissue throughout the breasts (about 40% of women)
  • Heterogeneously dense breasts (about 40% of women)
  • Extremely dense breasts (about 10% of women)

Those in the last two categories—heterogeneously and extremely dense breasts—are said to have dense breasts, which amounts to about half of women who are 40 years or older.

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Dense Breasts and Cancer Risk

Dense breast tissue is associated with a higher risk of developing breast cancer, though it’s not entirely clear why.

The same factor that makes some people's bodies create more breast tissue may also be the reason behind faster dividing cells and therefore a higher cancer risk, Dr. Leung said, but research and medicine doesn't yet know for sure.

As compared to those with predominantly fatty breasts, the risk of developing breast cancer for people with extremely dense breasts is up to four times higher, explained Renee Pinsky, MD, associate professor of radiology at Michigan Medicine.

Not only are people with dense breast tissue more likely to get breast cancer, but doctors may also have a harder time finding the tumor, due to how cancer shows up on mammograms.

"Cancers show up as white on a mammogram. Fibrous and glandular tissue also show up as white on a mammogram. So if you have dense breasts, it is harder to pick up a white-appearing cancer on a white background," Dr. Pinsky told Health. "It can make it harder to diagnose cancer in a dense breast."

Despite having an increased risk of breast cancer with dense breasts, they’re not the only risk factor. Other risk factors include age, family or personal history, and genetic mutations, as well as modifiable risk factors like smoking, drinking, or not being physically active.

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Why Additional Screenings Matter

Because people with dense breast tissue may have a harder time getting diagnosed with cancer early, it's important that these people get additional screenings, as Couric suggested.

This is typically done with magnetic resonance imaging (MRI) or with an ultrasound. An ultrasound—which was used to diagnose Couric's cancer—is also the most commonly used, said Dr. Leung. Though it can sometimes deliver false positive results, it does a good job of finding cancer for people with dense breast tissue.

"Ultrasound is sound waves, as opposed to a mammogram, [which] is X-rays," Dr. Leung said. Unlike the mammogram, on an ultrasound it's easier for doctors to tell tissue and tumors apart.

"The cancer looks dark, but the tissue looks relatively bright," she said. "That's actually a good thing for detection."

But other screening tests are not in place of a mammogram—they're in addition to it. The mammogram is critical to breast cancer diagnosis and will tell a doctor if a person has dense breasts and needs additional screening in the first place, Dr. Pinsky explained.

These screening tests should happen once yearly as soon as a woman with an average risk of breast cancer turns 40, according to the American College of Radiology and Society of Breast Imaging.

The American Cancer Society suggests the same, recommending yearly mammograms (or the option for a yearly mammogram) from ages 40 to 54. After that, mammograms can be done every other year. That cadence will likely hold, regardless of breast density.

"The point of screening is to detect cancers when they are still asymptomatic—before they become a problem, before the woman feels anything, before it affects her health, because that's when they tend to be very small and treatable, and hopefully curable," Dr. Leung said. "One of the strongest if not the strongest predictor of a good outcome of [a] cure—which is our ultimate goal—is early diagnosis."

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Accessing the Care You Need

As important as additional screening is for those with dense breast tissue, Couric raised alarm about the fact that getting this care isn't always easy.

"Currently, 38 states require doctors to notify their patients if they have dense breasts," she wrote. "But often that information doesn't clearly convey the need to have a supplemental screening."

"Meanwhile," Couric added, "only 14 states and the District of Columbia require insurance companies to fully or partially reimburse patients for the cost of potentially lifesaving breast ultrasounds."

Besides lack of awareness and cost, there are other health disparities that make Couric's swift diagnosis and treatment unattainable for all people who could be at risk of breast cancer.

Particularly, there are large health disparities for breast cancer along racial lines. Black women have a greater risk of having dense breast tissue in the first place, and are more than 2.5 times more likely to die of breast cancer than Asian and Pacific Islander women. Black women are also less likely to get screened with newer, more effective 3D mammography technology.

The differences in who has access to good quality mammograms—and the additional screening that may be necessary for those with dense breast tissue—could be attributed to a number of things. Dr. Leung said. Socioeconomic status, lifestyle, cultural perceptions of health care, urban or rural living, education level, and ability to take time off work can all play a role, she said.

It's important to also note that additional breast cancer screening has more than just financial costs—these tests can be anxiety-inducing for many, Dr. Leung said, so it's best to find a happy medium between getting proper cancer screening and acknowledging the barriers people have to overcome to get there.

In addition to getting additional screenings if a person has dense breasts, there are other things that can be controlled when it comes to breast cancer risk, including spreading awareness about dense breast tissue and additional screening, as well modifying lifestyle factors that could be worsening a person’s cancer risk. Having dense breasts is just one piece of the puzzle.

"Focus on the things that you could change, you could modify. And in fact, if you modify those other things—exercise, eating well, healthy weight—that's not just for breast cancer, that's for everything—colon cancer, diabetes, heart disease, hypertension, everything," Dr. Leung said. "I try to encourage my patients to think along those lines and not be despaired by dense breast tissue and not be scared by it."