Breast density is a measure of the amount of fibrous and glandular tissue in the breast compared to fatty tissue. It is an important factor in breast cancer risk and mammography interpretation, as dense breast tissue can make it more difficult to detect abnormalities on a mammogram.

Breast density is typically classified into four categories:

1. Nearly entirely fatty: This is the least dense category, with less than 25% glandular and fibrous tissue. Mammograms in this category are usually easier to interpret and abnormalities are easier to detect.

2. Scattered fibroglandular densities: This category has 25-50% glandular and fibrous tissue. Mammograms in this category may be more difficult to interpret, but abnormalities are still generally easier to detect.

3. Heterogeneously dense: This category has 50-75% glandular and fibrous tissue. Mammograms in this category may be more challenging to interpret, and abnormalities may be more difficult to detect.

4. Extremely dense: This is the most dense category, with more than 75% glandular and fibrous tissue. Mammograms in this category may be very difficult to interpret, and abnormalities may be difficult to detect.

It is important to note that breast density is not the same as breast size. A woman can have dense breasts and be small-breasted, or have less dense breasts and be large-breasted. Breast density is determined by the ratio of glandular and fibrous tissue to fatty tissue, not by the overall size of the breasts.

There are several factors that can affect breast density, including hormonal influences, genetics, and lifestyle factors such as diet and exercise. Some research suggests that taking estrogen and progesterone hormone replacement therapy after menopause may increase breast density, while other research suggests that breastfeeding may decrease breast density. However, more research is needed to fully understand the relationship between these factors and breast density.

It is important for women to be aware of their breast density and to discuss it with their healthcare provider, as dense breast tissue can increase the risk of breast cancer and may affect the accuracy of mammography. Women with dense breasts may be recommended to undergo additional screening tests, such as breast ultrasound or magnetic resonance imaging (MRI), to supplement mammography in order to detect abnormalities that may not be visible on a mammogram.

Breast density is a measure of the amount of glandular and fibrous tissue in the breast compared to fatty tissue. It can affect the accuracy of mammography and may increase the risk of breast cancer. It is important for women to be aware of their breast density and to discuss it with their healthcare provider.

October 2022.