What You Need to Know About Breast Density & Breast Cancer Risk

By Nicole Mercer Bolton, MD

If you've recently received a mammogram report mentioning "dense breasts," you may have questions about what that means and how it affects your health. Breast density is a normal finding, but it can influence both your breast cancer risk and how effectively mammograms detect cancer.

What does it mean to have dense breasts?

Breast density refers to the amount of fibroglandular tissue compared to fatty tissue in the breasts. It's categorized using the Breast Imaging Reporting and Data System (BI-RADS):

1. Almost entirely fatty: most of the tissue is fat.

2. Scattered areas of fibroglandular density: some dense areas, but most tissue is fat.

3. Heterogeneously dense: More areas of dense tissue, which may obscure small masses.

4. Extremely dense: Most of the tissue is dense with very little fat, which lowers mammography sensitivity.

The last two categories, heterogeneously dense and extremely dense, are considered dense. Dense tissues can make it harder to detect cancer on a mammogram and slightly increase breast cancer risk.

Your breast density is reported on your mammogram results. Federal law requires providers to notify patients if they have dense or non-dense breasts. You'll receive this information through MyChart or in a mailed letter after your mammogram.

Dense breasts are common and normal. About 40 percent of women over age 40 have dense tissue. Breast tissue tends to be denser in younger women and often becomes less dense after menopause.

Studies show that women with dense breasts have about twice the risk of developing breast cancer compared to women with less dense tissue. However, density alone doesn't place someone in a high-risk category. The main risk factors for developing breast cancer are being a woman and getting older.

Dense tissue can make it harder to detect non-calcified cancers on a mammogram. However, digital mammography and 3D mammography offer better cancer detection than traditional film mammography. 3D mammography takes multiple image "slices" through the breast, helping radiologists see past overlapping dense tissue. It can improve cancer detection and reduce false positives.

According to the Centers for Disease Control and Prevention (CDC), risk factors for breast cancer include both uncontrollable and controllable factors:

Uncontrollable risk factors:

• Increasing age (most diagnoses occur after age 50)

• Genetic mutations

• Family history of breast or ovarian cancer

• Early menstruation (before 12) or late menopause (after age 55)

• Late pregnancy (after age 30) or never having a full-term pregnancy

• Radiation exposure to the chest before age 30

Controllable risk factors:

• Lack of physical activity

• Post-menopausal obesity

• Some forms of hormone replacement therapy

• Not breastfeeding

• Alcohol consumption

Genetic testing is recommended for women with a personal or strong family history of breast or ovarian cancer, known genetic mutations in the family and certain related cancers. A genetic counselor can help determine if testing is right for you. However, dense breasts alone do not qualify you as high-risk.

The American College of Radiology (ACR) recommends women have their annual mammogram screenings starting at age 40 and earlier or additional screening (like breast MRI) for women at an elevated risk.

For women with dense tissue who want additional screening, breast MRI is the preferred option. Studies show MRI detects more cancers than ultrasound or 3D mammography alone.

If you notice a lump, bloody nipple discharge or any other breast changes, don't wait for your annual screening. Make an appointment to be seen by your primary care provider right away.

References:

• Society of Breast Imaging "Breast Density and Supplemental screening".

• Centers for Disease Control "Breast Cancer Risk Factors".

• Breast Cancer Screening for Women at Higher-Than-Average Risk: Updated Recommendations From the ACR. Monticciolo, Debra L. et al. Journal of the American College of Radiology, Volume 20, Issue 9, 902 - 914