How to know if you have ‘dense breasts’ that increase cancer risk

Are your boobs keeping secrets?

Today is “World Dense Breast Day,” raising awareness for a trait that increases cancer risk and makes tumors harder to detect using traditional screening methods — and it affects half of US women over 40.

“[It’s] like trying to spot a snowball in a snowstorm,” said Dr. Badri Konety, oncologic surgeon and chief medical officer of Astrin Biosciences, who told The Post about how new technology could finally help women catch what mammograms often miss.

What are dense breasts?

“Dense breasts refer to the internal composition of breast tissue as seen on a mammogram,” Konety explained.

Breasts are made up of two main parts: fatty tissue, which appears dark on a mammogram, and fibroglandular tissue, which shows up white. The more white tissue there is, the denser the breast.

“When breasts have more fibroglandular tissue relative to fatty tissue, they’re classified as dense,” he said.

Notably, breast size and density aren’t related.

“Smaller breasts can be extremely dense while larger breasts can be entirely fatty,” Konety said. 

Are some people more likely to have dense breasts?

Yes, with genetics, race and age playing a large role.

“For example, Asian women, while typically having less breast tissue overall, have a higher percentage of that tissue being dense,” Konety said.

“Black women, on the other hand, tend to have more breast tissue overall but a lower percentage of that is dense,” he noted.

Density is also something that can change significantly over the course of your life.

“Younger women are much more likely to have dense breasts, with density naturally declining after menopause,” Konety said. 

Why are dense breasts dangerous?

Breast cancer is the most common cancer in US women and the second deadliest, trailing only behind lung cancer, according to the American Cancer Society. In 2025, an estimated 317,000 American women will be diagnosed, and roughly 42,000 will die from the disease.

Many of those women will have dense breasts. Research shows women with extremely dense breast tissue are up to six times more likely to develop cancer than those with fattier breasts.

That increased risk, Konety said, comes down to biology.

“The fibroglandular tissue contains more cells that can potentially become cancerous — essentially, more cells means more opportunities for mutations,” he explained.

“It also has higher concentrations of growth factors and hormones that can promote tumor development,” he added.

On top of that, dense tissue fuels inflammation, messes with immune cells and boosts local estrogen levels, creating the perfect storm for precancerous lesions that may eventually turn deadly.

Why mammograms don’t always cut it

Studies show that mammograms can help find up to 98% of cancers in fatty breasts, but that number drops to as low as 30% for women with extremely dense tissue, according to Breastcancer.org.

The problem is all about visibility, Konety said.

“Both tumors and dense tissue appear white on mammograms, creating what radiologists call the ‘masking effect,’” he explained.

This can lead to interval cancers, or tumors found between routine screenings that were likely there but missed on the previous mammogram.

“Women with dense breasts have 2-5 times more interval cancers, and these tend to be discovered at later stages when they’re larger and potentially more aggressive,” Konety said. 

Dense breast tissue can also make it harder to differentiate between normal and abnormal areas, increasing false positives for mammograms. 

How can you tell if your breasts are dense?

Spoiler alert: You can’t feel it.

“Density is about internal architecture, not how breasts feel externally,” Konety said. “You can’t determine density through self-examination.”

Because dense breasts both raise cancer risk and make tumors harder to spot, the FDA now requires doctors to inform women about their breast density in mammogram result letters.

Breasts are classified by the BI-RADS system into four categories: A is almost entirely fatty, B has scattered fibroglandular tissue, C is heterogeneously dense, and D is extremely dense.

“The new federal notifications specifically state whether you have “dense” (category C or D) or “not dense” (category A or B) tissue and explain that density can hide cancers and increase risk,” Konety said.

“This information is typically available after your first mammogram, which current guidelines recommend starting at age 40,” he added. 

What to do if you have dense breasts

“Women with dense breasts need a more personalized, proactive screening plan,” Konety said.

After a mammogram shows density, he recommends asking your doctor about conducting a full risk assessment, like with CheckMate, to figure out your next steps.

Depending on your risk level, your provider may suggest ultrasounds or MRIs — though insurance doesn’t always cover them for for women without high-risk status.

There’s also new hope on the horizon.

“Companies such as Astrin Biosciences are developing blood tests that can be used reliably across all breast densities, including those with extremely dense tissue, to find signs of cancer early,” Konety said.

The test analyzes more than 7,000 proteins in a single blood sample, searching for cancer signals mammograms might overlook.

“Preliminary results are very encouraging — matching MRI-level performance from a simple blood draw,” Konety said.

“For the 42 million American women with dense breasts who’ve been told their mammograms might miss cancer but offered no practical alternatives, this represents a potential game-changer,” he added.

The blood test isn’t on the market just yet — but Konety said that doesn’t mean women should stay silent.

“Know your density, understand your options, and don’t accept ‘come back next year’ if you’re uncomfortable with mammography’s limitations in dense tissue,” he stressed.