Dense breasts are linked to an increased risk of breast cancer, but many people don’t know they have high breast density, even after having mammograms.

High density is normal, especially in younger women – though 40 per cent of women aged 40 – 74 have dense breasts.

According to the Breast Cancer Research Foundation, although the link between dense breasts and cancer isn’t yet fully understood, “breast cancer is known to develop in glandular tissue, so having a greater amount of it may simply provide more opportunity for abnormal cells to grow.”

Density is related to the amount of fibrous and glandular tissue tissue in the breast compared to the amount of fatty tissue.

Breast density and medical imaging

Dense breasts can make it harder to detect cancers in mammograms, as both cancers and density appear white in imaging. So while it can be relatively clear to see a bright white cancer spot among dark fatty tissue in an image, a cancer surrounded by dense fibrous and glandular tissue can go undetected. 

Speaking to the ABC, radiologist Professor Mary Rickard said mammograms are highly effective to detect early cancer, but added that reports can differ based on patients’ breast density. 

"A woman who's got low density breasts … has a very good chance that's a totally accurate report," she said.

"If she goes in with high density breasts, there is a significant risk that her cancer might be missed."

The Royal Australian and New Zealand College of Radiologists says additional imaging through ultrasounds, MRIs and contrast enhanced mammography can be helpful in detecting cancers that mammograms could miss in women with dense breasts. For example, unlike in a mammogram, cancers appear darker in ultrasounds, so they could potentially be more easily spotted. 

The European Society of Breast Imaging recommends women with high breast density receive an MRI every two to four years, as well as a mammography.  

As of last year, a statement describing the density of womens’ breasts and the possible impact this could have on imaging is attached to their report following mammograms in the US. But in Australia, whether you’re made aware of your breast density or not is dependent on where you live. 

Documenting breast density across Australia

In Western Australia, breast density has been reported by the state’s breast screening program for over ten years.

South Australia has also been informing patients if they have dense breasts since 2023, and Victoria will follow suit soon.

But BreastScreen Australia said it “should not routinely record breast density or provide supplemental testing for women with dense breasts”. Though a spokesperson for the Department of Health and Aged Care said this position is currently under review.

No BreastScreen programs recommend women with dense breasts have further imaging. 

Breast screening is life saving and free for women over 40 years old through BreastScreen Australia, but some experts and women who have been diagnosed with breast cancer are pushing for them, and similar screening services, to let people know if they have dense breasts following imaging.

Rickard said, “we're all entitled to know as much about our health as the doctor knows about our health".

Director of policy at the Breast Cancer Network of Australia, Vicky Durston agreed, insisting that "reporting of breast density empowers women … to make informed decisions that are right for them."