Breast density refers to the composition of the tissues within the breast. If a woman has dense breasts, it simply means that she has more fibroglandular tissue in her breast than fatty tissue. Younger women typically have denser breast tissue than older women, especially post-menopausal women.

Today’s mammogram reports categorize a woman’s breast density into four different categories as outlined by the BI-RADS® (Breast Imaging Reporting and Data System). The four categories are:

Category 1: Predominately fatty

Category 2: Scattered fibroglandular tissue

Category 3: Heterogeneously dense

Category 4: Extremely dense

Up to 40% of women have dense breasts and will be in the BI-RADS Category 3 or 4.

Why is this important? For reasons that are not yet fully understood, women with dense breasts may be at an increased risk for breast cancer. What’s more, dense breast tissue can obscure small cancers, limiting the sensitivity of mammograms.

Dr. Tracy Chen, a fellowship trained breast imaging specialist with RadX Imaging Partners, says that advances like 3D mammography have done much to improve screening capabilities in dense-breasted women. “3D mammography, or digital breast tomosynthesis, gives us more images and from different angles. It allows us to detect more cancers that might not appear on a conventional 2D mammogram,” she said.

Other screening options that women with dense breasts may wish to consider are breast ultrasound and breast MRI, two supplemental screening technologies which, when combined with mammography, are clinically shown to improve cancer detection rates in women with dense breasts.

In 2013, California was one of the first states to pass a breast density notification law that requires women with dense breasts to be notified in their screening mammogram report.

“Dense breasts are normal,” Dr. Chen says. “But it’s important that women with dense breasts talk to their doctors and take a closer look at their individual risk.”