Your Mammogram Report Now Includes Something New: Breast Density

Women getting mammograms in the United States now receive information that may not have appeared in their results before: whether they have dense breast tissue.

Since September 2024, federal rules have required mammography facilities to include breast density information in the results sent to patients.

For many women, the notification will say their breasts are “dense.”

That isn’t a diagnosis or an abnormal finding. About half of women over age 40 have dense breast tissue.

But knowing about it can be important because breast density can affect both a woman’s risk of developing breast cancer and how easily a cancer can be seen on a mammogram.

What Does Having Dense Breasts Mean?

Breasts contain different types of tissue, including fat, fibrous tissue, and glandular tissue.

Breast density describes the proportion of those tissues.

A breast with relatively more fibrous and glandular tissue and less fat is considered denser. Density tends to be greater in younger women, although it varies from person to person and can change over time.

A woman generally can’t determine her breast density by how her breasts look or feel. It is determined from a mammogram.

Density matters more when you look at how different tissue appears on the mammogram.

Fatty breast tissue appears relatively dark.

Dense breast tissue appears white.

Unfortunately, tumors can also appear white.

That creates a problem similar to trying to find one white object against another white background.

According to the National Cancer Institute, mammograms are less sensitive in women with dense breasts because abnormal areas can be more difficult to distinguish from surrounding tissue.

As a result, mammography alone may miss some cancers.

Density also matters for another reason. Having dense breasts is itself a risk factor for developing breast cancer.

Those are two separate issues: dense tissue can make a cancer more difficult to see, and women with dense breasts have a higher risk of developing breast cancer than women with less-dense breasts.

Your Letter Doesn’t Tell You Everything

The new federal notification includes an important detail women may not realize.

Radiologists don’t actually divide breast density into only two groups.

They use four categories.

However, the patient notification simplifies those categories to “dense” or “not dense.”

The mammography report provided to the referring healthcare provider includes the more specific breast density category.

That means a woman who receives a letter saying she has dense breasts may want to ask her provider which of the four density categories applies to her.

That can provide more context than the notification alone.

Breast density isn’t necessarily permanent, either. A woman’s density can change over time, which is another reason mammography assesses it rather than treating it as a lifelong designation.

Does Dense Tissue Mean More Testing Is Needed?

The federal rule doesn’t automatically recommend additional imaging for every woman with dense breasts.

Instead, the notification alerts women that additional imaging studies may help find cancers in some people with dense tissue and encourages them to discuss their individual situation with a healthcare provider.

That distinction is important.

Breast density is one factor in breast cancer risk, but it isn’t the only one. Age, family history, and other individual risk factors can also affect screening decisions.

The purpose of the notification is to ensure women know their breast density and can include that information in conversations about their care.

For someone receiving a mammogram result, “dense” doesn’t mean cancer was found.

It also doesn’t mean something is wrong with the breast.

It means the breast contains a greater proportion of fibrous and glandular tissue, which can make mammograms more difficult to interpret and is associated with increased breast cancer risk.

While the notification provides basic information, women who want to know more may need to ask.

The mammography report sent to the healthcare provider contains the specific density category.

That makes a simple question useful after receiving the results: What is my actual breast density category, and does it change what screening is appropriate for me?