Dense Breast Tissue: What It Means and What To Do Next

Here is what you need to know about breast density: what it is, how it is measured, whether it raises your risk of developing breast cancer and what to do next.

What Is Dense Breast Tissue?

Breasts are made up of three types of tissue:

• Glandular tissue (which provides milk)
• Fibrous connective tissue (which gives the breast its structure)
• Fatty tissue

Dense breast tissue means a person has more glandular and fibrous tissue than fatty tissue. Density is detected on a mammogram. It cannot be felt during a breast self-exam or a clinical exam.

How Is Breast Density Determined?

Radiologists look at density using the Breast Imaging Reporting and Data System, known as BI-RADS. This was developed by the American College of Radiology. There are four categories of breast density:

• Almost entirely fatty: Very little dense tissue is present.
• Scattered fibroglandular density: Small areas of dense tissue are scattered throughout the breast.
• Heterogeneously dense: Many areas of dense tissue are present. This is one of two categories classified as "dense."
• Extremely dense: The breast is almost entirely made of dense tissue. This is the highest density category.

People in the last two categories — heterogeneously dense or extremely dense breasts — are considered to have dense breast tissue. About 40% to 50% of people who get mammograms fall into one of these groups.

"Dense breast tissue is extremely common. It is not a disease. But it is clinically important because it can both modestly increase breast cancer risk and make breast cancers more difficult to find on a mammogram," says Georgia G. Spear, MD, breast radiologist and chief and vice chair of breast imaging at Northwestern Medicine. "Breast density is only part of your risk profile. Screening decisions should be personalized rather than one-size-fits-all.”

Who Is More Likely to Have Dense Breasts?

Several factors are associated with higher breast density:

• Age: Density is typically higher in younger people. It tends to decrease after menopause, as glandular tissue is slowly replaced by fat.
• Hormone use: People who use hormone therapy after menopause may maintain or develop higher density.
• Genetics: Breast density tends to run in families.
• Body weight: People with lower body weight often have denser breasts because fatty tissue is less prevalent.
• Pregnancy and breastfeeding: Density can temporarily increase during and after pregnancy.

Most of these factors cannot be changed, which is why it is important to stay on top of screening.

Does Dense Breast Tissue Increase Breast Cancer Risk?

Yes. Having dense breast tissue is considered an independent risk factor for breast cancer.

• People with heterogeneously dense or extremely dense breasts have a higher risk of developing breast cancer compared to people with mostly fatty breasts.
• Those with extremely dense breasts have roughly four to six times the risk of people with the least dense breasts — though their overall individual risk may still remain low.

Scientists believe this increased risk is due to the greater amount of glandular tissue, which is where many breast cancers develop.

Dense breast tissue alone does not mean a person will get cancer. It is one factor among many —age, family history, prior biopsies and genetic variants, such as BRCA1 and BRCA2 — that contribute to overall risk.

Why Dense Tissue Makes Mammograms More Challenging

On a mammogram, both dense tissue and many cancers appear white. This can make it harder to spot cancers in people with dense breasts. Imagine trying to find a snowball against a snowy background.

Mammograms are still the recommended primary screening tool for breast cancer screening. However, in those with dense breasts, cancers may be harder to find with mammography alone. This is why breast density matters when planning a screening approach.

Should People With Dense Breasts Consider Additional Screening?

Depending on your overall risk, your care team may recommend supplemental screening with 3D ultrasound or MRI alongside a standard mammogram.

Common options include:

• Breast ultrasound: A breast ultrasound uses sound waves to create images of breast tissue. It can help find masses that may not show up on a mammogram. It is often the first supplemental option considered for people with dense breasts and average overall risk.
• Breast MRI: Breast MRI is typically used for people with a higher overall risk of breast cancer, such as those with a known BRCA mutation, a strong family history or prior chest radiation. It is more sensitive than mammography but also more likely to produce false positives. This can lead to additional imaging or biopsy.

Advanced imaging technologies, including 3D automated breast ultrasound (ABUS), abbreviated and ultrafast breast MRI techniques, and artificial intelligence (AI)-assisted imaging analysis may also help improve cancer detection in patients with dense breast tissue.

“We are entering a more personalized era of breast cancer screening,” says Dr. Spear. “Advanced technologies, such as 3D automated breast ultrasound, abbreviated and ultrafast breast MRI, and AI-assisted imaging analysis, are helping us better evaluate dense breast tissue and improve supplemental screening for appropriate patients.”

Are There Downsides to Extra Screening?

Any screening test comes with trade-offs, but screening can save lives by helping detect cancer when it is easier to treat.

“Mammograms remain the foundation of breast cancer screening. They can save lives through early detection,” says Dr. Spear. “For some patients with dense breast tissue, supplemental screening may provide additional benefits. But those decisions should always balance improved detection with the possibility of false positives, additional imaging and unnecessary biopsies.”

What Breast Density Notification Laws Mean for You

Federal law now requires that all mammogram reports notify patients about their breast density. If your report says you have dense breasts, you will receive additional information explaining what that means.

This is not a cause for alarm. It is information that can help you have a more informed conversation with your care team about your personal risk and screening options.

Questions To Ask Your Doctor

After learning you have dense breast tissue, consider asking:

• Which category of breast density do I have?
• Based on my overall risk factors, should I consider supplemental screening?
• What are the benefits and potential downsides of additional imaging for me specifically?
• How often should I be screened, and with what tests?
• Is there anything else I should know about my breast health?

Making Sense of Dense Breasts

Learning you have dense breast tissue can feel unsettling — but it is a common, normal finding. Dense breasts are not a diagnosis. They are one piece of information that helps you and your care team build a screening plan that is right for you.

Learn more about your breast health and screening options.