Breast Density

A description of the relative amount of glandular tissue versus fat in the breast. The higher the proportion of fibroglandular tissue, the denser the breast (Source:

Categories of Breast Density

A. Fatty
B. Scattered Areas of Density
C. Heterogeneously Dense
D. Extremely Dense

<25% dense tissue
25-49% dense tissue
50-74% dense tissue
75-100% dense tissue

Dense Breasts

Breasts that have more fibroglandular tissue than fat. Categories C and D are considered to be dense breasts. Dense tissue appears white on a mammogram and so does cancer, creating a masking effect..


Breast density assessment software used primarily in Nova Scotia and paid for by the federal government. Women in Nova Scotia are not told their density and neither are their doctors, despite the software.

Extremely Dense

One of two categories used by radiologists to describe dense breasts. About 10% of women, aged 40- 74 years, fall into this category. Most of the breast tissue consists of glandular tissue, creating a white out effect and making it extremely difficult to see cancer.

Heterogeneously Dense

One of two categories used by radiologists to categorize dense breasts. About 40% of women, aged 40-74,  fall into this category. Large portions of the breast consist of glandular tissue, making it hard to detect cancer.

Interval Cancer

A cancer detected in between mammogram screenings- missed by mammogram and discovered when a lump is felt by the woman or doctor. Interval cancers are more aggressive and later stage cancers. Women with the highest category of density have an 18x higher chance of having an interval cancer.


It uses magnetic fields, radio frequency pulses, and a computer to produce detailed images of the breast. MRI is used to screen women deemed to be high risk.

Node Negative

Cancer has not spread to the lymph nodes. Early detection is key for best survival outcomes.


Radiologists assess density visually and the level of density may vary from one radiologist to next. Subjectivity can be eliminated using software.


Also known as 3D Mammogram- more effective than 2D for heterogeneously dense breasts, but research is showing it is not effective for women in highest category of density. Tomosynthesis reduces the number of call backs.


Uses sound waves to image the breast. It is not routinely used as a screening tool, but rather used as a diagnostic tool if something questionable is seen on mammogram. Numerous studies show ultrasound detects additional 3-4 cancers per thousand women missed by mammogram. While Hand Held Ultrasound is predominantly used, some clinics in Alberta are using 3D Automated Breast ultrasound (ABUS).

Medical Disclaimer

The Dense Breasts Canada website is intended for the general purpose of:
1. Raising awareness about dense breasts and
2. Encouraging advocacy for the reporting of dense breast tissue to women.
We have included references, where applicable to ensure that the information provided is evidence based. However, we cannot guarantee that the information on the site is error-free or complete. The website is not intended to be a substitute for medical advice from a doctor. For answers to specific health-related questions, please consult your doctor. While we speak of Automated Breast Ultrasound (ABUS), we are not affiliated in any financial way with any private clinics that offer ABUS.