Breast density

Breast density is important in determining breast cancer screening approaches. Breast tissue can be fatty or made of thick, fibrous tissue and milk glands or combinations of the two types. All types of density are considered normal. Breast density is assessed using a standard measuring system known as BI-RADS. It is more difficult to see and detect all cancers in dense breasts on mammograms. Also, breast cancer occurs more frequently in dense than fatty breasts (Eng et al., 2014).

Boyd et al (2007) compared mammogram results of women with breast density of less than 10% with women with density of 75% or more. Women with breast density of 75% or more were 17.8 times more likely to have breast cancer detected within 12 months of screening.

Some researchers have found a genetic link to breast density.

Typically breast density increases in women in their 30s and decreases in their 40s. About 20% of women, however, have excess collagen in the breast that leads to the density remaining in the breasts.

Researchers (Zhang, et al, 2013) have identified a protein (DDR2) on the surface of breast cancer tumors. When this protein binds with the excess collagen the cellular pathway of cancer metastasis (EMT) open and stay open longer allowing tumor cells to spread to blood vessels and the lymphatic system. This DDR2 protein has been found to be present in 70% of invasive ductal carcinomas.

Levels of breast density

There are four levels of breast density:

There are four levels of breast density:
Level 1: Almost all fatty tissue (1 out of 10 women)
Level 2: Scattered areas of dense tissue, but mostly fatty tissue (4 out of 10 women)
Level 3: Mixed dense and fatty tissue, also called heterogeneous (4 out of 10 women)
Level 4: Extremely dense tissue (1 out of 10 women)

In addition to overall density of a breast, researchers are investigating the significance of variation in mammographic density. To date they have found the amount of variation also increases the risk of breast cancer.


Mammographic density

Examples of variation in mammographic density:
(A) 0%,
(B) <10%,
(C) <25%,
(D) <50%,
(E) <75%,
(F) >75%.
(G) illustration of a computer-assisted measure.

The outer (red) line shows the edge of the breast, the inner (green) line shows the edge of dense tissue. Percent density is calculated by dividing the dense area by the total area and multiplying by 100 (Boyd, et al., 2010).

Reproduced with permission

State laws regarding density notification

To date 27 states have passed breast density notification laws with legislation proposed in additional states. These laws require information about breast density of the individual and the risks posed by breast density be reported in writing to women who have undergone mammography (Dehkordy & Carlos, 2013).




This content will be reviewed or retired by 12/2019