Breast density (also called mammographic density) is a term used to describe how breasts look on a mammogram. It measures and compares the different types of breast tissue. Breast density cannot be seen or felt in a clinical examination by a doctor.
The types of tissue that make up the breast and can be seen on a mammogram are:
On a mammogram, fatty tissue appears as dark areas, while glandular and connective tissues appear white. Cancers also appear as white on a mammogram.
Breasts that have a lot of glandular and connective tissue are described as dense. The expression "having dense breasts" is used to refer to people who have high mammographic density. Men tend to have less glandular and connective tissue in the breast than women, so breast density does not generally pose an issue for men.
Breast density is important because it can have serious implications for people who have dense breast tissue.
The glandular and connective breast tissue can hide (or mask) cancers in a mammogram, making early detection difficult. This is because cancers, glandular tissue and connective tissue all appear as white on a mammogram. Thus, cancers can be “hidden” by the healthy tissue in a mammogram.
People with dense breasts are at increased risk of having cancers missed on a mammogram and, therefore, at increased risk of having an ”interval” cancer. Interval cancers are cancers that are found between scheduled screening mammograms. They are usually diagnosed after a woman presents to her doctor with symptoms (e.g. a lump, nipple discharge, etc). Because they are detected later, interval cancers may require more treatment and may have poorer outcomes.
The Information Forum on Mammographic Density (INFORMD), has a video that helps explain breast density and why it is important.
Having dense breasts is a risk factor for developing breast cancer. Breast density should be considered with a person’s other breast cancer risk factors to estimate their risk of developing breast cancer and to advise on screening and management. Read more on this in the section "Breast cancer risk" below.
Breast size does not relate to how dense your breast tissue appears on a mammogram. Density depends on how much fat your breast has compared with how much glandular/connective tissue.
The level of breast density can be scored by radiologists (specialists who read mammograms) along a scale from very low density (mostly fatty tissue) to mostly dense (mostly glandular/connective tissue).
One of the most commonly used scales is the American College of Radiology’s Breast Imaging Reporting and Data System (BI-RADS), which radiologists use to classify breast density as A, B, C or D. Sometimes a numerical scale of 1, 2, 3 or 4 is used.
The BI-RADS system defines breast density in the following categories:
Several factors can influence breast density to some extent. For example, young women and those with a lower body mass index (BMI) tend to have higher mammographic density.
Genetic factors are also important in determining the level of breast density. It is heritable, so people in the same family are likely to have similar density.
Other factors that can increase or decrease breast density to some extent include:
These factors can change hormone levels in the body and influence breast density. However, while breast density usually declines with age, environmental influences or hormone levels, density is mostly determined when the breasts first form.
This means some people will always sit in a high-density category compared with others in their age group, while others will always have lower breast density.
Research has shown that higher breast density is not only a contributing factor in masking breast cancers in mammograms, but also a risk factor for developing breast cancer.
People with heterogeneously or extremely dense breasts (Types C and D on the BI-RADS scale, see above) have a higher risk of developing breast cancer than women with fattier breasts.
Breast density should be considered with other risk factors, such as family history and the age of diagnosis of other family members, to help determine a person’s risk of developing breast cancer.
It is important to note, however, that:
Most BreastScreen services do not advise people of their mammographic density. BreastScreen in Western Australia and South Australia are the only two states that currently notify people if they are identified as having dense breasts when they have their screening mammograms.
The people who are notified as having dense breasts are given follow-up information, including whether any further care or investigation is necessary.
Don't be afraid to ask your doctor about your breast density. People have the right to know their breast density, their breast cancer risks and how sensitive a mammogram is at detecting cancers in dense breasts.
People have the right to make informed decisions about breast cancer screening and their own health.
Some private screening clinics tell people about their breast density. However, you may need to pay to have a mammogram done privately. Talk to your GP if you think this is something you would like to do.
Mammograms remain the recommended screening tool to detect breast cancers, despite the potential for some small cancers to be missed.
Many cancers can be seen on a mammogram, even if you have dense breasts. There is currently not enough evidence to include additional screening modalities in the clinical guidelines. Clinical trials are being undertaken to look at adding other screening methods such as ultrasound and MRI to enhance the detection of breast cancers.
However, anyone with very high breast density (Type D on the BI-RADS scale, see above) and other risk factors should discuss supplementary screening options such as ultrasound or MRI with their doctor.
Access further information through INFORMD (Information Forum on Mammographic Density) .
Read the Clinical Oncology Society of Australia (COSA) position statement on breast density.
Read personal stories from BCNA members who share a similar experience with breast density: Kate Keogh Murray on Mammographic density and screening.
Visit My Journey, BCNA’s online tool for information tailored to your diagnosis.
Join our Online Network if you think that talking to others online and sharing experiences will help.
Contact BCNA’s Helpline on 1800 500 258 between 9.00 am and 5.00 pm AEST Monday to Friday, for information about the services and support that may be available for you and your family.
Let’s be Upfront about navigating a breast cancer diagnosis as an Aboriginal or Torres Strait Islander.
Let’s be Upfront about living with breast cancer at a young age with Sofi Leota.
Episode 16: Young women and triple negative breast cancer
*This article does not provide medical advice and is intended for informational purposes only.
Please consult a medical professional or healthcare provider if you're seeking medical advice, diagnoses, or treatment.