Dense Breasts and What They Mean for Screening

The simple versionExplain▾

Breasts are made of three kinds of tissue: glandular tissue, fibrous connective tissue, and fatty tissue. Breast density describes the balance of these on a mammogram. Breasts are called dense when they have relatively high amounts of glandular and fibrous tissue and relatively low amounts of fatty tissue.

Dense breasts are common and normal — not a disease or an abnormal condition. In fact, nearly half of women 40 and older who get mammograms are found to have dense breasts.

Dense breasts are common and normal — but they do affect how mammograms are read and your risk picture.

You can't feel itExplain▾

One surprising fact: you cannot feel breast density, and neither can your doctor during a physical exam. Density isn't about how your breasts feel or how firm they are.

The only way to know is through a mammogram. A radiologist — a doctor who reads medical images — looks at the mammogram and classifies the density. This is why density is sometimes called "mammographically dense."

Only a mammogram, read by a radiologist, can reveal breast density — you can't detect it yourself.

How density is categorizedExplain▾

Radiologists use a system called BI-RADS to describe breast density in four categories, from mostly fatty to extremely dense:

• Almost entirely fatty — about 10% of women
• Scattered areas of dense tissue — about 40%
• Many areas of dense tissue (heterogeneously dense) — about 40%
• Extremely dense — about 10%

If your mammogram report says you have dense breasts, it means you fall into one of the two densest categories.

How density affects a mammogramExplain▾

Here is why density matters for reading a mammogram. On the image:

• Dense tissue appears white
• Some abnormal changes, like tumors, also appear white
• Fatty tissue appears dark

Because dense tissue and possible problems both look white, a problem can be harder to spot — like finding something white against a white background. This makes mammograms less sensitive in dense breasts, meaning they are more likely to miss a cancer. People with dense breasts may also be called back for follow-up testing more often.

Dense tissue and tumors both look white on a mammogram, so cancers are easier to miss.

Density and breast cancer riskExplain▾

Separate from the effect on reading a mammogram, dense breasts are also a risk factor for breast cancer. Women with dense breasts have a higher risk than women with mostly fatty breasts.

It's important to keep this in perspective. Density is one of several risk factors, and it is a modest one. Some factors, like using menopausal hormone therapy, are linked to higher density; others, like increasing age and having had children, are linked to lower density. Your doctor can help you understand your overall risk.

One reassuring point: research shows that people with breast cancer who have dense breasts are no more likely to die from it than those with fatty breasts, after accounting for other factors.

Dense breasts modestly raise risk — but they don't make breast cancer more deadly.

Notification laws and extra imagingExplain▾

Because density affects screening, updated U.S. FDA regulations now require mammography providers to inform you if your mammogram shows dense breasts. If you receive such a notice, it's a good prompt to talk with your care team.

You may wonder whether you need extra imaging, such as an ultrasound or MRI. According to the U.S. Preventive Services Task Force, there isn't yet enough evidence to recommend for or against additional imaging just because someone has dense breasts. Whether it makes sense depends on your full risk picture — so this is a conversation to have with your doctor.

A density notice is a cue to talk with your doctor about your overall risk and whether extra imaging fits you.