Breast Density: What Is Its Real Impact?

CHIGACO - The facts are irrefutable. Women who have dense breast tissue have a higher risk of developing breast cancer throughout their lifetimes. But, what does this mean for how radiology should approach this issue in the future?

As the extent to which dense breast issue impacts breast imaging and cancer diagnosis is still emerging, it’s critical that radiologists learn more about assessing risk, communicating results of dense breast tissue with patients, and supplemental imaging options, said industry experts at RSNA 2013.  

“There is, indeed, a need for a forward-looking, standardized, evidence-based approach to dealing with dense breast tissue. And, should women be told that part of their mammogram is normal, but that we can’t say all of it is?” said Robert Smith, PhD, a cancer epidemiologist and senior director of cancer control for the American Cancer Society. “Much of legislation contains an argument about women’s rights to a complete exam. But, we must factor in what women want. There’s an enormous concern about false positives. But if women are prepared to endure that, we need to consider it as a factor.”

Roughly half of all women have dense breast tissue that includes an increased volume – and types – of collagen and fibroblasts that make it easy for cancers to hide and potentially go undetected. Women with dense breast tissue are roughly four times as likely to develop breast cancer during their lives. In fact, recent research attributes 16 percent to 28 percent of all breast cancers to dense tissue. 

Risk Assessment

In many ways, said Jennifer Harvey, MD, radiology professor at the University of Virginia School of Medicine, understanding breast density can be as complicated - and important - as having a clear idea of your cholesterol level.

“Although most of you have a ball park idea of your total blood serum, hopefully, you also know your LDL, HDL, and triglyceride levels,” she said. “But, you really need to learn more about overall cholesterol. Just like what you really need to learn about it breast density.”

The relationship between breast density and cancer risk, she said, is linear. However, like height, there are several genetic factors that determine whether a woman will have dense breast tissue, making it a complicated factor in breast cancer research and treatment.

But research has uncovered a few things about the risk dense breast tissue poses.

For example, determining risk for obese women can be tricky, Harvey said. Obesity is a risk factor for breast cancer, but it’s independent of dense breast tissue. To figure out a woman’s true risk, any calculations must be adjusted for body mass index (BMI).

“If you look at unadjusted odds ratios for BMI, very obese women have a two-fold increase of breast cancer,” Harvey said. “But, when you adjust for BMI, the risk goes up to four-and-a-half times the risk among obese women.”

In addition, dense breast tissue can continue to affect a woman even after her diagnosis on through her treatment. If a women with dense breast tissue receives the drug tamoxifen as part of her breast cancer treatment, her risk of recurrence can drop by 63 percent – but only if her breast density decreases. Unfortunately, Harvey said, if the breast density remains the same or increase, tamoxifen exposure create a two-fold risk that the woman will experience a recurrence or death.

Monitoring Breast Density

Keeping track of breast density to estimate a woman’s breast cancer risk isn’t the only reason to keep an eye on the tissue, said Martin Yaffe, PhD, a medical biophysics professor at Sunnybrook Health Sciences Center. Doing so is also useful in determining how much impact the dense tissue has on the efficacy of mammography and other breast imaging modalities.

“There’s a suggestion that the sensitivity of mammography is lower in women with dense breast tissue. We should be using that information to produce more optimized strategies for screening,” he said. “That way we can identify women at low risk and screen them less intensively while using additional resources for women at medium and high risk, such as ultrasound or tomosynthesis.”

Currently, a cancer that appears between screenings is 17.5 times more likely to happen to a woman with dense breast tissue, Yaffe said. So, finding a way to bolster screening for women with dense breast tissue could help radiologists and referring physicians diagnose breast cancers earlier.

Supplemental Imaging

Despite talk of using tomosynthesis and ultrasound to screen women with dense breast who’ve already undergone a mammogram, it’s important to remember that mammography is still considered the gold standard for breast cancer detection.

“No one is talking about replace mammography,” said Wendie Berg, MD, PhD, radiology professor at the University of Pittsburgh. “But there’s a lot of discussion about high-risk women for whom mammography is known to have lower sensitivity. We find their cancers at later stages. The cancers are larger, and there’s more metastatic disease. For these reasons, they’ve been the initial focus of supplemental screening.”

It’s important to know how effective the supplemental options are, however, before selecting one. According to Berg, ultrasound will find an additional three or four cancers per 1,000 scans; tomosynthesis, an additional two per 1,000; MRI, an additional 10 per 1,000, and molecular breast imaging, an additional seven to eight per 1,000.

For women with extremely dense breast tissue, though, tomosynthesis might not be effective, she said. Tomosynthesis can, indeed, detect a mass, but ultrasound can show the same mass along with anything else close-by that might be irregular. MRI, she said, can go into even greater detail.

Ultimately, said Virginia’s Harvey, the most important thing to do while the industry continues to research the impact of dense breast tissue, is to remind patients that they must be screened annually.

“Mammography works. It saves lives, and we have to keep repeating that to patients,” she said. “They need to come in every year and get an exam. If we can get down below 30-percent mortality, then we need to and can do more.”