“We are pleased to inform you that your recent mammogram … shows no sign of cancer.”

This sentence often elicits a sigh of relief from women reading their mammogram results, but about half of them will go on to read a sentence that isn’t so comforting: “Your mammogram indicates that you do have dense breast tissue.”

The letter then typically explains that dense breast tissue makes mammograms harder to read and that the patient “could benefit from additional screening.”

Rather than relief, this part sparks questions. What is dense breast tissue? How serious is it? What does “additional screening” look like?

“It leaves me thinking maybe I’m not as in the clear as I think I am,” said Martha Thomas, a Utahn who has received the density notification.

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In early March, the Food and Drug Administration announced a requirement for medical practices to tell patients when their mammograms show dense breast tissue, which will take effect later this year. Breast density notification has been required by law in Utah since 2018.

Still, women with dense breast tissue often don’t know what to do when they find out — many don’t even know what it means.

What is breast density?

Breast density is essentially the proportion of milk-producing glands to fat in the breasts. The more glandular tissue a woman has in her breasts, the “denser” they are.

“So it doesn’t have anything to do with how the breast tissue feels to someone’s fingers or how it looks to your eyes,” said Dr. Cindy Matsen, a physician at the Huntsman Cancer Institute at the University of Utah.

There are four categories of breast density, based on the amount of glandular tissue a woman has. Patients are notified of their density when they fall in categories three or four.

Breast density is mostly a result of genetic makeup, according to Kathryn Everton, a radiologist who specializes in breast imaging at St. Mark’s Hospital; however, age and body type also play a role.

“Younger women — premenopausal women — tend to have more dense breast tissue overall, because their ovaries are still producing estrogen,” Everton said. “And slender women actually tend to have denser breast tissue and less fat in their breasts.”

Dense tissue typically decreases gradually after menopause, but breasts can stay dense if a woman uses a hormonal treatment.

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Why do you need to know if you have dense breast tissue?

Dense breast tissue is common — about 50% of women over 40 have it — but it presents two problems. First, it makes finding cancer more difficult.

“Dense tissue shows up as white on a mammogram, and tumors and other things that we’re looking for also show up as white,” Matsen said.

Everton compared reading a mammogram of dense breast tissue to looking for a snowman in a snowstorm, while a mammogram of a breast that’s mostly fat is like looking into “a clear pool of water.”

The second problem is that dense breast tissue can increase risk for breast cancer.

“It doesn’t necessarily increase your risk nearly as much as having a family history or having a genetic mutation,” Everton said. “It only slightly increases most women’s risk.” However, in some cases, dense breast tissue can cause women to go from intermediate to high risk for breast cancer.

What should you do if you have dense breasts?

Aside from recommending a conversation with a primary care provider and “additional screening,” most post-mammogram letters do not give recipients with dense breast tissue much guidance.

“It’s so hard for women to know what to do next,” Matsen said. “They kind of get this letter, and they’re like, ‘OK, I have dense breasts — what am I supposed to do?’”

Everton says the first step is not to panic — “It’s not like you’re abnormal. It’s not like there’s anything you can do to control it.”

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After talking to a primary care doctor or gynecologist, there are two main options for supplementary screening: ultrasound and MRI.

In a screening breast ultrasound, or sonogram, either a handheld device or an automated machine uses sound waves to detect abnormalities that the mammogram missed. One downside to ultrasounds is that they find abnormalities that aren’t cancer, which may prompt even more testing, like biopsies, for some women.

MRIs are even more sensitive than sonograms. “It’s basically a test that uses magnetic waves and a little bit of contrast in your veins, and it looks at blood flow to the tissue of both breasts,” Everton said.

A screening breast MRI costs more than an ultrasound, but it is the recommended supplementary test for women with high risk for breast cancer.

Catherine Graham, an Intermountain Health patient, chose to get an MRI after she discovered that she had dense breast tissue, and said she was surprised by how expensive the test was.

“I was a little sticker shocked,” Graham said. “I think I paid like $1,000 out of my own pocket for it.”

But recently, Intermountain has made available a less costly version called an abbreviated MRI, which doctors are recommending for women at higher risk for breast cancer.

Despite the federal legislation requiring medical practices to alert women of their breast density, Everton pointed out that there is work to be done when it comes to resources for women with dense breast tissue.

“There’s this huge gap in notification and then assisting women in finding an additional screening test, if they choose it, that their insurance will cover,” she said.

No matter a patient’s breast density, Everton recommends that they conduct monthly self-breast exams and continue with yearly mammograms.

“Nothing can replace a mammogram in terms of the mortality benefit,” she said. “Mammograms are proven to save lives, and you can’t replace it with MRI — although a lot of women would love that — because it can find earlier signs of cancer that even an MRI can’t in some cases.”

Those with questions about breast density can visit densebreast-info.org or connect with a cancer information specialist at the University of Utah.