The issue of breast density has been a hot topic over the last several years.  Many women are told they have “dense breasts” on their mammograms, but most are not sure what that means.

Breast density refers to the amount of fibrous and glandular tissue that appears on a woman’s mammogram. The fibrous and glandular breast tissue seen on a mammogram is white. The fatty tissue on a mammogram appears dark. A woman with dense breast tissue will have more fibrous and glandular tissue than fatty tissue and so her mammogram will appear more white. A woman whose breast tissue is primarily fatty replaced will have a mammogram that looks more dark. 

There are 4 categories of breast density (also called a density score) that a radiologist uses for describing a patient’s mammogram:

• Class A (or 1): Fatty
• Class B (or 2): Scattered fibroglandular density
• Class C (or 3): Heterogeneously dense
• Class D (or 4): Extremely dense

How does breast tissue density affect a radiologist’s ability to detect breast cancer? A cancerous lump can show up as white on a mammogram. Calcifications, which may sometimes be associated with breast cancer or DCIS (ductal carcinoma in-situ), also appear white on a mammogram. If the patient’s breast tissue is dense it may be like trying to find a snowball in a blizzard.  The higher the breast density level the more intense the “blizzard” is.  High tissue density can make it harder to see certain changes on a mammogram that might ultimately be a cancer. 

For women with very dense breast tissue, other screening methods for detecting breast cancer may be recommended in addition to or in place of digital screening mammography. 3-D Mammography, or tomosynthesis generates more detailed image of the breast using reconstructed 2 dimensional images. This may be recommended instead of digital screening mammography for some patients. Ultrasound is another tool that can greatly aid in cases of increased breast density. Hand-held ultrasound screening or automated whole breast ultrasound exams may be recommended in women with dense breast tissue. MRI is another tool that can show very detailed images of the breast and can be helpful in the setting of high breast density in patients whose lifetime risk for developing breast cancer is over 20%.  

When comparing women who have extremely dense breasts to women who have fatty replaced breasts, the risk of developing breast cancer in women with dense breasts is increased by 4 to 6 times.  So knowing one’s breast tissue density may be used to help a woman develop her own personalized plan in breast cancer screening and in healthy lifestyle choices to reduce her risk of breast cancer.