IIn 2017, 55-year-old Leslie Ferris Yerger underwent a routine mammogram and breast ultrasound. Both came back clear. Two months later she had an unrelated Dexa scan to measure her bone density. The technician noticed an abnormality in her hip. After additional testing, Yerger was diagnosed with stage four breast cancer – an advanced stage of the disease in which the cancer has spread beyond the breasts.
The mammogram and ultrasound had not picked up the cancer, as Yerger would learn, because of her dense breast tissue.
“My cancer simply wasn’t in those photos,” she says. “I also learned that it is not an unusual story.”
According to the National Cancer Instituteshows that about 50% of women age 40 or older have dense breasts, a term that refers to the ratio of fatty tissue to denser fibrous and glandular tissue in a person’s breast. During a mammogram, dense tissue can make it difficult for technicians to see potential cancerous growths.
While some U.S. states require mammography reports to include information about a patient’s breast density and how it could potentially affect results, there was no federal rule until this year.
In September, the FDA began requiring mammogram reports to include information about breast density and how it can affect patient outcomes. “Dense tissue makes it more difficult to find breast cancer on a mammogram and also increases the risk of developing breast cancer,” the release said. The report says that “in some people with dense tissue, other imaging tests besides a mammogram may help detect cancer.”
The ruling marks a turning point in the field of breast cancer detection and treatment. But there is no agreement yet on what these results mean for screening in the US or abroad. In Great Britain, for example, the NHS does not include breast density information on patient mammogram reports.
Experts say more research and testing is needed in the future, as well as patient self-defense. Here’s what you need to know.
What are dense breasts?
Breasts are composed of three types of tissue: fatty breast tissue, fibrous connective tissue and glandular tissue. These last two, collectively referred to as “fibroglandular tissue‘are denser than adipose tissue. The ratio of fibroglandular tissue to fatty tissue determines whether or not breasts are considered compact; a person with dense breasts has more fibroglandular tissue in relation to fat. This determination is not based on a specific ratio, but on the radiologist’s subjective assessment, explains Dr. Habib Rahbar, professor of radiology at the University of Washington.
There are four categories of breast density. The first two – completely fatty breast tissue and scattered fibroglandular breast tissue – are considered low density. The other two – heterogeneous breast tissue (which about 40% of women have) and extremely dense breast tissue (which about 10% of women have) – are considered dense.
Despite its prevalence, “there is much that is not understood about breast density and why some people have denser breasts than others,” says Dr. Angela DeMichele, professor of medicine and co-leader of the breast cancer program at the University of Pennsylvania’s Abramson Cancer Division. center.
People from certain racial groups, such as Asian Americans and Black Americans, are more likely to have dense breast tissue, says Dr. Arif Kamal, chief patient officer for the American Cancer Society. It can also run in families.
Additionally, an individual’s breast density can vary from year to year depending on age, hormone levels, menstrual cycle, and medications. While roughly 50% of women in their 40s have dense breasts, that number drops to about 25% in women over 60, says Dr. Maryam Lustberg, chief of medical oncology at Yale Cancer Center.
How do you find out if you have dense breasts?
To find out if you have dense breasts, you should have a mammogram. A radiologist will then examine the results and determine your breast density. As a result of the FDA’s new ruling, these findings will be included in your mammogram report, along with guidance on whether to request additional testing.
Breast tightness isn’t something you can diagnose yourself, Kamal says. “It says, ‘When I look at the screen (of a mammogram), your breasts are closed.’ That doesn’t mean you can feel the difference.”
How does breast density affect cancer screening?
A higher density of this fibroglandular tissue can make reading mammograms more difficult. Mammograms are X-rays, and X-rays penetrate soft tissue, such as fat, more easily, making these areas appear dark on the resulting image. Tissue with a higher density appears whiter and darkens the field of the mammogram, making it more difficult for a radiologist to identify suspicious masses, which also appear white. Lustberg compares it to trying to see through a “blizzard.”
For people with dense breasts, doctors often recommend other imaging in addition to mammograms. This may include a whole breast ultrasound, which uses sound waves instead of X-rays to create an image of the breast. “It’s a different modality, so if there’s a mass behind something, (the sound wave) will bounce a little differently,” Lustberg explains. However, experts disagree on how useful breast ultrasounds are; one described them as “limited value”.
Some doctors also recommend that patients with dense breasts undergo an MRI, which is an effective way to detect cancer even in extremely dense breasts. But MRIs can lead to false positives. Lustberg says this risk may be justified for people at increased risk of breast cancer. MRIs can also help determine whether a mammogram is accurate. But for people at average risk, MRIs can result in “unnecessary biopsies” and “increased anxiety.”
Kamal says balancing these factors in additional testing comes down to “the patient’s risk tolerance.”
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“It’s very confusing,” DeMichele said. “We haven’t had a definitive study yet that showed us exactly the right test to do in (people) with dense breasts that could (detect) cancers without also leading to more cancers and more biopsies.”
Complicating the problem is unequal access, Rahbar says. Such tests are not always covered by insurance, and some patients live in so-called “medical deserts” where advanced or even basic imaging technologies may not be available.
Are mammograms still useful?
Does all this mean that mammograms are useless for people with dense breasts? Not at all, experts say.
In addition to detecting dense masses, mammograms also detect calcifications in the breast. “This is one of the best ways to find a very small cancer,” says DeMichele, especially cancers that don’t normally show up in densities. Although these calcifications are a little harder to see on mammograms of dense breasts, they are still “very visible,” she says.
Does breast density affect a person’s risk of cancer?
Breast density itself is a risk factor for cancer, although experts aren’t entirely sure why.
People with dense breasts are two to three times more likely to develop breast cancer during their lifetime, Lustberg says. There are a number of hypotheses as to why this might be so, but none have been conclusively proven. “Dense breasts appear to have a slightly different biology than fatty breast tissue,” says Lustberg.
Experts emphasize that a person’s breast density is only one potential risk factor. Breast cancer risk assessment tools, some of which are available online, take into account factors such as a person’s age, how old they were when they first got their period, how old they were when they first had a child, and their family history of cancer .
“I think it is every woman’s right to know her own personal risk of breast cancer,” says Lustberg.
How can patients advocate for themselves when it comes to breast density?
Without clear, standardized guidelines for breast density screening, much of the responsibility falls on patients to get the information they need.
“We shouldn’t wait for the scientific community to figure out with one voice what it wants to do. There is no time for that,” says Kamal. Instead, he says, patients should insist on conversations with their doctors to understand their risk for breast cancer, and advocate for the care and tests they feel comfortable with.
Yerger founded the advocacy organization My Density Matters in 2021. Groups like these have been raising awareness about breast density for years. They also provide information about breast density, as well as questions to ask health care providers, additional screening options, and advice on how to address potential opposition from doctors and insurance companies.
“What we (patients) ask is not easy,” says Yerger. “Right now that’s what we have to do.”