Like many women, Shamma Mullen breathes a sigh of relief every time she gets good news about the results of her latest mammogram. Two years ago, however, Mullen’s doctor sent her additional information that alarmed her.

She had dense breasts.

“I had never seen a letter like that before and had no idea what having dense breasts even meant,” said Mullen, 38, of Andover, Massachusetts. Mullen immediately went online to search for more information, and called her doctor with questions about follow-up tests.

Women age 40 and older in every state are now receiving notifications about their breast density along with their standard mammogram report, due to a new rule from the Food and Drug Administration. Massachusetts and 38 other states have already been sending notifications about breast density, which reflects the proportion of milk glands and connective tissue to fatty tissue. The FDA requirement standardizes those messages.

Dense tissue makes it harder to find breast cancer on a mammogram; and that dense breast tissue is a risk factor for cancer.

You’ve got dense breasts. Now what?

Mammogram studies show that almost half of women over age 40 have dense breasts.

Going forward, women with dense breasts will be encouraged to talk to their doctors and told that “other imaging tests in addition to a mammogram may help find cancers.”

Some health advocates argue that the notifications have oversimplified a complex issue. They argue that without clear, evidence-based instructions, women could be left scared, confused and frustrated.

Judith Garber, a senior policy analyst at the Lown Institute, a nonpartisan health policy think tank, notes that there is no national standard for following up on dense breast reports.

That means women will get different advice, depending on their doctor.

While some doctors will urge women to undergo extra tests  — such as additional mammograms, ultrasounds or MRIs — others will advise women to simply continue getting regular mammograms, said Dr. Mark Pearlman, an emeritus professor at the University of Michigan Medical School, who has written screening guidelines for the American College of Obstetricians and Gynecologists and the National Comprehensive Cancer Network.

“You cannot counsel an entire population of women with dense breasts with one policy that’s going to be appropriate for everybody,” Pearlman said.

Whether a woman can get additional imaging may depend on insurance, which doesn’t always cover them, said Robert Smith, an epidemiologist and senior vice president of cancer screening at the American Cancer Society.

Smith said it’s important for women to know if they have dense breast tissue.

Radiologists sort breast tissue into four groups: 

• Extremely dense 
• Mostly dense 
• Mostly fatty
• Almost entirely fatty. 

Because breast cancers can hide behind dense tissue, “these cancers can be growing and getting larger and more advanced until they finally peek out of the corner of that density and you can see them” on a mammogram, Smith said. “When the diagnosis takes place, it’s not an early one.”

Smith added, “if the breast is completely dense, the conventional technologies just simply aren’t very accurate and supplemental imaging is needed.”

Dr. Hilary Marston, the FDA’s chief medical officer, said the notifications will empower women.

“We really wanted to make sure that women had the information that they needed in plain language to make good decisions for their own health,” Marston said. “The most important thing is to make sure that people have the information in a high-quality way that’s communicated clearly.”

Benefits and risks of additional screening

Part of the confusion is that experts disagree whether women with dense breasts need extra imaging.

Although the American College of Radiology and National Comprehensive Cancer Network recommend that women and their doctors consider supplemental screening, two other influential groups — the American College of Obstetricians & Gynecologists and the U.S. Preventive Services Task Force — say there’s not enough evidence of benefit to recommend additional tests.

And while additional tests can detect more cancers than mammograms alone, there’s no evidence that extra testing saves lives, said Dr. Nancy Keating, professor of health care policy at Harvard Medical School.

“We don’t know that outcomes are going to be any better” by adding more tests, Keating said. “We don’t know that additional imaging has benefits that outweigh the harms.”

Additional imaging — such as ultrasounds and MRIs — carry risks, Garber said. Both tests can lead to “false alarms,” in which benign tissue is flagged as suspicious.

False alarms can lead to invasive biopsies that can be painful and cause bleeding, as well as stressful and unnecessary follow-up tests, some of which involve additional radiation exposure or dyes that can cause side effects and allergic reactions.

In some cases, additional screenings can lead women to be diagnosed and treated for cancers that would never have bothered them, problems known as overdiagnosis and overtreatment.

A study published in 2022 estimated that 15% of mammogram-detected breast cancers in women age 50 to 74 were overdiagnosed. Ruth Etzioni, a biostatistician at the Fred Hutchinson Cancer Center and a co-author of the study, notes that not all cancers are the same. While some aggressive tumors grow quickly and need immediate treatment, others grow too slowly to harm women in their lifetime. Older women who are diagnosed with a slow-growing breast tumor can die of another cause before the cancer would have caused problems.

Some research also casts doubt on the reliability of the system used to label breasts as dense or not dense. A review article in Annals of Internal Medicine found that 13% to 19% of women were reclassified into a different breast density category — from dense to nondense or vice versa — on their subsequent screening mammogram.

Crissy Matos said she underwent her first mammogram at 40, but received her first dense breast notification this year at 42. Matos, who lives in Stroudsburg, Pennsylvania, said she wonders why her breasts didn’t look dense on her first mammogram, given that breasts tend to be denser in younger women.

Doctors recommended a second mammogram, this time using a newer technology known as digital breast tomosynthesis, often called 3-D mammography. An ultrasound showed that the suspicious area on her mammogram was nothing to worry about, Matos said. 

The high cost of advanced imaging puts it out of reach for many patients. Women from rural areas or marginalized communities often lack access to the latest technology.

Garber, the analyst from Lown Institute, said that some of the FDA’s language is misleading. Although it’s true that women with dense breasts are 1.5 to 2 times more likely than other women to develop breast cancer, they’re no more likely to die from it.

The FDA’s “notification language is sort of pushing people toward doing more tests, when, in fact, the tests aren’t actually recommended” universally, Garber said. “So the FDA is saying ‘you have this breast density, you should be aware that you have an additional risk factor.’ But then there’s not really anything that people should do about it. It’s a really terrible place to be as a patient.”

The FDA’s Marston said she hopes women and their doctors will use the density notifications to have informed conversations. “We certainly don’t want to hide the information from women,” Marston said.

Given the uncertainty about the benefits of additional screening, Pearlman said “the safest and probably most accurate” way to advise women with dense breasts is to say, “We don’t know for sure what the best practice is at this point.”

Mullen said she was relieved when follow-up tests — which were covered by insurance — found nothing suspicious. But breast cancer “is always on the top of my mind because of my family history,” Mullen said. Now that she knows her breasts are dense, “I think I would be nervous if I didn’t do an ultrasound.”