Dense Breasts: What Your Report Means

Breast density is a measure of how much fibrous and glandular tissue there is in the breast compared with fat. It has nothing to do with breast size or firmness, and you cannot tell by touch. It is seen only on a mammogram.

Radiologists describe density in four groups: almost entirely fatty, scattered areas of density, heterogeneously dense, and extremely dense. The last two count as dense. According to the American Cancer Society, about half of women who have screening mammograms fall into one of them.

Since September 10, 2024, a federal rule requires every mammogram report sent to a patient in the United States to state whether the breasts are dense or not dense. If this is the first time you have seen it on a report, that is why. Your breasts have not changed; the reporting has.

There are two separate reasons. First, women with dense breasts have a higher risk of breast cancer than women with fatty breasts, though it is not clear why. Second, dense tissue appears white on a mammogram, and so do tumors, which makes cancers harder to see.

Dense breasts are a risk factor, not a diagnosis. They are one item in your overall picture, alongside age, family history and the other risk factors.

This is where the honest answer is that experts disagree. The American Cancer Society says that, at this time, experts do not agree on what other tests, if any, should be done in addition to mammograms in women with dense breasts. The U.S. Preventive Services Task Force found the evidence insufficient to recommend for or against supplemental screening with ultrasound or MRI on the basis of density alone.

What is known: 3D mammography, ultrasound and MRI can each find some cancers a standard mammogram misses, and each brings more false alarms. Insurance coverage for extra tests also varies. Density combined with other risk factors, such as a strong family history, changes the calculation.

Keep having mammograms. Most breast cancers can be seen on a mammogram even in dense breasts, and the Task Force's schedule applies to women with dense breasts the same as everyone else. See the screening guidelines.

Ask whether your imaging center uses 3D mammography. The American Cancer Society says it appears to be helpful in women with dense breasts.

Bring your report to a screening visit. We look at your density alongside your other risk factors and talk through whether additional imaging is worth asking for, and what your plan is likely to cover.