All about breast density

The association between breast density and the risk of breast cancer has been studied and validated over the past twenty years. It is now clearly demonstrated that high breast density increases the risk of developing breast cancer. But what exactly is it? How is breast density measured?

We decipher breast density for you.

Definition of breast density

Breast density is assessed on the basis of a mammography examination. It corresponds to the proportion and density of fibrous tissue (which appears white on the mammogram image) in relation to fatty tissue (which appears black on the mammogram image). The breast contains a mammary gland and supporting tissue that contains vessels, fibres and fat. The more dense and fibrous tissue the breast contains, the greater the breast density.

Classification of breast density

In 1995, the ACR-BI-RADS classification was introduced which divided the breasts into four categories. This classification has been updated several times. Since 2005, the density categories according to BI-RADS V are as follows:

Category A: The breasts are almost entirely made up of fat and contain very little fibrous tissue.
Category B: The breasts contain some areas of fibrous tissue, thus increasing the breast density.
Category C: The breasts are heterogeneously dense with equal or almost equal amounts of fat and fibrous tissue. This may mask small masses.
Category D: The breasts are extremely dense. The breasts are predominantly composed of fibrous tissue. This reduces the sensitivity of the mammogram.
Factors influencing breast density

Mammographic density is a “biomarker” summarising the hormonal history of each woman at a given time. Breast density decreases with age, but certain risk factors for breast cancer are also associated with breast density: breast density is generally higher in women who have not had children, or who have had a late first pregnancy, or who have a high alcohol intake.

How can breast density be assessed?

Breast density can only be assessed by mammography. Indeed, it highlights dark areas corresponding to fatty tissue and light areas corresponding to fibrous tissue, allowing the radiologist to determine the density of the breast. If the breasts have different densities, the radiologist will choose the higher density.

While it is the density assessed by the radiologist’s eye that correlates with the risk of breast cancer, this assessment poses problems of reproducibility with significant variations from one radiologist to another.

To address this problem, some companies such as Predilife are marketing solutions that automatically determine breast density from mammography examinations using artificial intelligence algorithms.

Link between breast density and breast cancer

Breast density plays a dual role:

it has both a masking effect that can make it difficult for the radiologist to read the image, which may miss the tumour
it is a risk factor for breast cancer

For women with high breast density, the risk of finding breast cancer after a screening mammogram is higher in the year following screening. These are some interval cancers that were present at the time of the mammogram but are difficult to detect because they are “hidden” by the high density of the breast.

Women with the highest density are 4 to 6 times more likely to develop breast cancer than women whose breasts are almost entirely composed of fatty tissue.

Today, it is possible to assess one’s risk of breast cancer at 5 years. Breast density is a factor that must be taken into account for a reliable assessment. Do not hesitate to ask your doctor for information and to get tested.