By Sharp Grossmont Hospital Health News Team

If you’ve had a mammogram and were told you have dense breasts, you’re not alone. Most women have some breast density, but why does it matter?

“Women who have dense breasts are four to five times more likely to develop breast cancer than women with low breast density,” said Dr. Tere Trout, a board-certified diagnostic radiologist affiliated with Sharp Grossmont Hospital.

“It’s unclear whether this increased risk is related to the fact that mammograms with dense breast tissue are more difficult to interpret or whether more glandular tissue itself leads to the increased risk,” she said.

What defines density is the appearance of breast tissue on a mammogram. Breasts are composed of both fatty and glandular elements — those breasts with more fatty tissue are less dense, while those with more glandular tissue are denser.

“Breast density is a measure of the proportion of the different tissues that make up a woman’s breasts and how the breasts look on a mammogram,” Dr. Trout said. “There are four categories: mostly fatty; scattered tissue; heterogeneously dense; and extremely dense.”

Mammograms of denser breasts are harder for a radiologist to interpret than mammograms of fatty breasts because the breast tissue may obscure lesions of interest.

To better understand, consider the visual of finding a polar bear in a snowy background. Glandular tissue looks white or light gray. Because cancer can also appear white on a mammogram, it’s harder to interpret because it blends in. On the other hand, fatty breast tissue appears more transparent on a mammogram, so lesions are less difficult to detect.

Roughly 50 percent of women undergoing screening mammography are classified as having either heterogeneously dense or extremely dense breasts. Depending on individual risk factors, additional screening might be needed.

Federal law requires mammography centers in many states, including California, to report breast density information to physicians and patients. Knowing an individual’s breast density will help to better assess risk and guide decision-making about how often to screen using mammography.

Dr. Trout notes that at this time, there are no special recommendations or screening guidelines for women with dense breasts. However, some studies have suggested breast tomosynthesis may find a few more breast cancers than 2-D mammography alone. The exact benefit is still under investigation.

“Women with dense breast tissue should speak with their health care provider so that he or she can assess other risk factors. If a patient is felt to be at increased risk for breast cancer, additional tests may include a breast ultrasound or a breast MRI,” Dr. Trout said.

— This article features experts from Sharp Grossmont Hospital. For more health stories, visit sharp.com/news.