Mammographic density and what it means

What does this mean?

Breasts are made up of milk glands and fat, held together by a fine mesh of fibrous tissue.

Some women have very few milk glands scattered throughout the fat, while others have many glands packed tightly together. This is what we call dense glandular tissue. Dense glandular tissue presents two main problems in the diagnosis of breast conditions.

1. Small abnormalities, including cancers, may be hidden in dense glandular tissue and can be more difficult to see on your mammogram.
2. For reasons we don’t completely understand yet, tightly packed milk glands are more likely to develop the abnormalities that might, in the long term, lead to breast cancer. In other words, dense glandular tissue is a risk factor for breast cancer.

What is my Density?

We grade mammograms for density according to the number of milk glands:

• Category A – very few milk glands
• Category B – average number and density of milk gland
• Category C – densely packed milk glands
• Category D – extremely densely packed milk glands

Most women have category or A or B density. Fewer women have category C or D

How does having dense tissue change how I look after my breasts?

We look after women with Category C and D mammographic density differently to women with lower density breast tissue.

Firstly, we recommend you have an ultrasound along with your mammogram, to detect anything that may be ‘hiding’ in the dense tissue. We also recommend you have a mammogram every year instead of every 2 years.

Will I always have Dense Tissue?

Breast density does reduce over time, especially after menopause.

Before menopause, oestrogen keeps the milk glands active. At menopause oestrogen levels gradually fall and the milk glands shrink. Some shrink so much they virtually disappear. This means that glandular density thins out – a bit like a forest thinning out. How much thinning occurs varies between women, and is hard to predict. Some women with Category D mammograms will gradually thin out to a Category B density, while others might just go from the very top of a Category D density to the bottom of Category D.

So if my mammograms are so hard to read, why not just have an ultrasound?

Unfortunately, some cancers will only show up on a mammogram and not be seen on an ultrasound, while others will only show up on the ultrasound and not be seen on a mammogram. For this reason, it is best practice for women with dense breast tissue to have both a mammogram and an ultrasound.

We hope this helps you understand why the screening plan we recommend for you is different from the plan your friends or relatives may be following.

If you have any other questions about your breast density, please ask your breast doctor today.