Breast cancer blood test can predict treatment response

A new blood test developed by the Institute of Cancer Research predicts how well patients with advanced breast cancer will respond to targeted therapies. 

A new blood test can predict how well patients with advanced breast cancer will respond to targeted therapies even before treatment begins. 

A team from the Institute of Cancer Research, London, used a liquid biopsy to detect the presence of tiny amounts of cancer DNA in the blood at the start of treatment and four weeks into the treatment. They compared the levels of this DNA with patients’ outcomes, including how long it took for a cancer to grow, and how well the cancer was responding to treatment.

The researchers, based at the Breast Cancer Now Toby Robins Research Centre at The Institute of Cancer Research, saw a strong association between low levels of circulating tumour DNA (ctDNA) at the start of treatment and treatment response. A similar association was seen after four weeks, one treatment cycle.

The results show that it is possible to monitor how well treatment is working through a non-invasive blood test, meaning patients who are not responding well could be identified and moved to alternative treatments sooner.

“Our study shows that a simple blood test could give us an early and reliable indication of whether treatment is working for people with metastatic breast cancer,” said study lead Nicholas Turner, professor of molecular oncology at the Institute of Cancer Research, London, and consultant medical oncologist at The Royal Marsden NHS Foundation Trust. 

“By tracking changes in tumour DNA in the blood just a few weeks into treatment, we can begin to identify who is likely to benefit and who may need a different approach sooner. This has the potential to make treatment decisions faster, more personalised and ultimately more effective for people living with metastatic breast cancer,” he added. 

In the study, funded by Breast Cancer Now, Cancer Research UK, and the NIHR Biomedical Research Centre at The Royal Marsden NHS Foundation Trust and the Institute of Cancer Research, the team analysed blood samples from 167 people with advanced breast cancer.

The patients were enrolled in the plasmaMATCH trial – a study run by the ICR’s Clinical Trials and Statistics Unit (ICR-CTSU), and funded by Stand Up To Cancer, a joint fundraising campaign from Cancer Research UK and Channel 4.

The team grouped the patients based on their type of breast cancer and the specific mutations in their genes.

The first group consisted of patients whose cancers had an ESR1, HER2, AKT1, AKT or PTEN mutation, and who received targeted treatments matched to those mutations. The second group consisted of people with triple-negative breast cancer and no targetable mutation. These people received a combination of the PARP inhibitor olarparib and the ATR inhibitor ceralasertib.

For patients in the second group, low ctDNA levels before treatment began were associated with longer progression-free survival – 10.2 months, compared with 4.4 months. In this group, the percentage of patients who responded to treatment – either seeing their tumours shrink or disappear – was 40% for those with low ctDNA levels, compared with 9.7% for those with higher levels.

A similar, but weaker, association was also observed between pre-treatment ctDNA levels and clinical outcomes in the first group.

In the second group, the blood test after four weeks of treatment also showed a strong link between ctDNA levels and patient outcomes. Patients whose ctDNA was no longer detectable had their cancer kept at bay for 12 months, compared with 4.3 months in patients who still had detectable ctDNA. Treatment response was also significantly higher for those with undetectable ctDNA, with 85.7% responding to therapy, versus 11.4% among those with detectable ctDNA.

The researchers now hope to validate their findings in larger studies.