COMMON QUESTIONS ABOUT DENSE BREASTS

WHAT IS BREAST DENSITY?

Dense breast tissue is a common clinical finding that can only be assessed by mammography, affecting nearly half of people over 40 who are scanned. Dense breasts have less fat and more glandular and fibrous tissue. Unfortunately, they also make a mammogram harder to read, so smaller cancers may be hidden. As breast cancer tends to grow in dense breast tissue more often than fatty breast tissue, dense breasts also increase your risk for cancer.

HOW IS BREAST DENSITY MEASURED? 

Breast density is described by a letter scale, using the Breast Imaging Reporting and Data System (BI-RADS).

• A – Almost entirely fatty:There is almost no dense tissue, which makes abnormalities easy to detect. About 10% of women are in this category.
• B- Scattered fibroglandular densities:Scattered areas of density, but the majority of tissue is fatty. About 40% of women are in this category.
• C – Heterogeneously dense:More than half the breast is dense tissue. About 40% of women are in this category.
• D – Extremely dense:Nearly all of the tissue is dense. About 10% of women are in this category.

HOW DOES BREAST DENSITY AFFECT MY MAMMOGRAM?

Glandular and fibrous tissue, which make up a higher percentage of tissue in dense breasts, appear as white clusters on a mammogram. Cancer also typically appears as a white cluster, and so it can be hard to see when surrounded by dense tissue.

WHAT FACTORS AFFECT BREAST DENSITY?

Having dense breasts is common and can even change over time. Increased estrogen levels in the body encourages the growth and multiplication of breast cells, which can lead to increased density.

Dense breasts are more commonly found in younger people, or older people who take hormone replacement therapy (HRT). There are many additional factors that can affect breast density, such as having a low body mass index, which increases your chance of having dense breasts.

Lifestyle factors such as alcohol consumption can increase your percentage of dense tissue, as alcohol consumption can increase estrogen levels.

WHAT DOES THIS MEAN FOR MY CANCER RISK?

Dense breast tissue is a risk factor for breast cancer. According to the Canadian Cancer Society, women with dense breast tissue have a higher risk of developing breast cancer than people with little or no dense breast tissue. However, women with dense breasts are no more likely to die from breast cancer than someone who does not have them.

WHY GET SCREENED AT MAYFAIR?

At Mayfair Diagnostics, our mammogram machines use 3D mammography (tomosynthesis) and are equipped with software that classifies breast density. Once your exam is completed, your images will be reviewed by a radiologist who will compile a report that is sent to your doctor. When an assessment determines that breast density is high, the radiologist may suggest annual mammography exams. In addition, the radiologist may suggest the use of handheld or automated breast ultrasound (ABUS) in conjunction with your regular screening mammogram.

Mammography views the breast in slices and provides a greater level of detail, while breast ultrasound increases the sensitivity of the scan.

Mayfair offers 3D mammography and diagnostic breast ultrasound services in Alberta at 13 clinics in Calgary, one in Cochrane and at our Regina location in Saskatchewan. ABUS is only offered in Calgary at our Market Mall, Mayfair Place, Southcentre, and The CORE locations.

REFERENCES

Canadian Cancer Society (2024) “Breast density.” www.cancer.ca. Accessed March 12, 2025.

Healthwise Staff (2023) “Dense Breasts” myhealth.alberta.ca. Accessed March 12, 2025.
Mayo Clinic (2024) “Dense breast tissue: What it means to have dense breasts” www.mayoclinic.org. Accessed March 12, 2025.