Breast density “not just a technical feature of imaging"
16 February 2026
Not only does having dense breasts make it harder to spot cancer in a mammogram, Peter Mac-led research has found dense breasts promote more aggressive cancer growth and could be a factor when personalising treatment.
The research, led by Associate Professor Kara Britt and Dr Dane Cheasley, has identified important biological differences in the tumour microenvironment when comparing breast cancers from high versus low density breasts.
The findings, published in the journal npj Breast Cancer, come after screening guidelines were recently updated to ensure Australian women with dense breasts are informed of this when receiving their mammogram result.
Both dense tissue and early-stage cancers appear as white on a mammogram.
“Our research reinforces that mammographic density is not just a technical feature of imaging,” explains Dr Cheasley, who is a Senior Research Scientist within the Women's Cancer Program at Peter Mac.
“It is a biological factor with real implications for cancer behaviour, detection and, potentially, treatment.”
The research identified elevated numbers of immune cells – such as CD8+ and CD4+ T cells and B cells – had infiltrated the tissue at the edge of tumours in dense breasts.
While these cells are key drivers of the body’s immune response, they can also be co-opted by the cancer in ways that support rather than prevent tumour growth.
Higher density breasts were also seen to have an increased genomic instability – or an increased tendency for DNA mutations and genetic alterations during cell division, a known trigger for cancer.
“We found that tumours arising in dense breast tissue are more immunologically active, with increased adaptive immune cell infiltration,” Associate Professor Britt says.
“The greater genomic instability and immune activity could influence response to treatment, and particularly immune-based or targeted approaches.”
In a future where breast cancer care is becoming increasingly risk-stratified and personalised, breast density could be an additional factor to consider when optimising treatment.
The paper is titled “Breast cancers arising in high mammographic density tissue harbor tumor-promoting immune profiles” and you can read it in full online here.
In Australia, around 40 per cent of women aged 50 –74 who attend BreastScreen meet criteria for having dense breasts. The findings help to explain the elevated breast cancer risk seen in these women, noting their cancers are typically harder to detect.
For more information about breast density, check the website for InforMD – a group co-founded by Associate Professor Britt.
Peter Mac also has a free online tool to help women understand their personal breast cancer risk, iPrevent. It considers breast density and provides a personalised report you can discuss with your doctor.
Peter Mac’s PCMed telehealth service is also available, via referral from a GP or specialist doctor, for a discussion
about medications that can reduce breast density and decrease the chance of getting breast cancer.
Media who would like more information on this story can contact the Peter Mac Communications team on 0417 123 048.