Breast Tissue Density and Breast Cancer Risk: Understanding the Link

Content medically reviewed by Carolyn Olson, APRN, CNP

When you have a screening mammogram, the results tell your health care provider whether there are any suspicious areas that could be signs of cancer. But there is other valuable information you should pay attention to in the report: your breast tissue density.

“Having dense breast tissue is associated with an increased risk of breast cancer,” said Carolyn Olson, nurse practitioner at Essentia Health. “Dense breasts also make it harder for providers to spot abnormalities in mammograms, as dense tissue can obscure small masses.”

Knowing your breast density can help your radiologist or primary care provider understand whether you need any further screening in addition to your regular mammogram. 

What Does It Mean to Have Dense Breast Tissue?

Your breasts are made up of different kinds of tissue – 

• Glandular tissue is made up of lobes and tubes, which make and carry milk.
• Fibrous connective tissue holds breast tissue in place. 
• Fibroglandular tissue is a combination of glandular and fibrous tissues.
• Fatty breast tissue gives breasts their size and shape by filling in the spaces between glandular and fibrous tissue.

Breast density is not related to the size or firmness of your breasts. Women with dense breasts have lower amounts of fatty tissue and higher amounts of glandular and fibrous connective tissue, which are harder to see through on a mammogram.

Why Do Some Women Have Dense Breasts?

Several factors can determine your breast density. 

“Younger women typically have more dense tissue,” Olson said. “Older women or those who are postmenopausal may have more fatty replacement of their dense tissue as their estrogen levels drop.”

In addition to age, breast density can be affected by –

• Low body mass index (BMI). The lower your BMI, the less fatty tissue you have, which means you could have more dense breast tissue. Therapy for menopause symptoms. Using hormone replacement therapy can lead to more dense breast tissue.
• Pregnancy. Women who are pregnant generally have higher breast density.
• Breastfeeding. A history of breastfeeding can affect breast density.

How a Mammogram Shows Your Breast Density

If you have dense breasts, you can’t feel it when doing self-exams, and your health care provider also can’t determine how dense your breasts are by examining you. The only way to know your breast tissue density is through a mammogram.

The radiologist, which is a doctor who interprets medical imaging, reads your mammogram and includes your breast density in the report. There are four categories –

• Category A: Breasts have mostly fatty tissue. About 10% of women are in this category.
• Category B: There are scattered areas of dense glandular and fibrous connective breast tissue (which appear white on a mammogram). About 40% of women are in this category.
• Category C: Breasts are heterogeneously dense, which means many areas of dense glandular and fibrous connective breast tissue appear on the mammogram. Another 40% of women fall into this category.
• Category D: Breasts are extremely dense and are almost all dense glandular and fibrous connective tissue. About 10% of women have extremely dense breasts.

Those in categories C and D are considered to have dense breasts.

Dense Breasts and Breast Cancer Risk

If you have dense breast tissue, you are at an increased risk for developing breast cancer. Researchers aren’t sure why this is the case, although it may be because dense tissue is made of fibroglandular tissue and breast cancers develop in glandular tissue. The Essentia Health High-Risk Breast Cancer Program can offer an assessment of your personal and family risk to see if you are at high risk of developing breast cancer.

The average woman has a 12 to 13% chance of getting breast cancer in her lifetime. A high-risk individual has a greater than 20% lifetime risk of developing breast cancer. Expert staff members can also help form personalized plans of care. 

When you have dense tissue, it can be harder for radiologists to detect suspicious areas on a mammogram because both dense tissue and breast cancers appear similarly. A 3D mammogram can provide a more comprehensive look at your breast tissue. 3D mammograms are often covered by insurance. 

Regardless of whether you have dense breasts, you should follow guidelines for getting regular mammograms. 

“Many cancers are visible on mammograms even if you have dense breast tissue,” Olson said. “The best practice for everyone is to have annual mammograms starting at age 40, as well as yearly clinical exams, in addition to performing monthly breast self-exams. This is a proactive approach to your breast health.”

Women who have dense breasts and meet criteria for our high-risk program might be good candidates for additional imaging –

• A family history of breast cancer—one first degree or two or more second degree relatives on the same side
• Relatives with a genetic mutation associated with breast cancer risk
• A history of having chest radiation for a childhood cancer
• A history of high-risk breast lesions, such as atypical hyperplasia or lobular carcinoma in situ

Talk with your provider about whether you should have any additional screening for breast cancer.