LONDON, Jan 19: Scientists have developed a simple DNA blood test that can predict how patients with breast cancer are likely to respond to treatment, potentially allowing doctors to offer the most effective therapy from the outset.

The test, known as a liquid biopsy, analyses circulating tumour DNA (ctDNA) released into the blood by cancer cells. It was trialled on 167 patients with advanced breast cancer at the Institute of Cancer Research (ICR), London. Blood samples were taken before treatment and four weeks after a single treatment cycle.

Dr. Iseult Browne, a clinical research fellow at the ICR and first author of the study, said: “Our study shows that a simple blood test measuring circulating tumour DNA can provide an early prediction of whether a patient’s breast cancer will respond to treatment.

“Knowing this at the earliest stage – in this case, at the start of treatment, or after just four weeks – means that we can avoid giving patients drugs that won’t work and provide them with alternatives before their cancer has a chance to grow. For example, they could be given an alternative targeted therapy, a combination of drugs, or even enrolled in a clinical trial to test a novel drug. Trials are now underway to see if adapting a patient’s treatment based on these early blood tests does indeed improve their outcome – giving them more time living well with their cancer kept at bay.”

Patients were divided into two groups based on cancer type and mutations. The first group included patients with ESR1, HER2, AKT1, AKT, or PTEN mutations who received targeted therapies matched to their mutations. The second group consisted of patients with triple-negative breast cancer, an aggressive form of the disease, who were treated with a combination of the PARP inhibitor olarparib and the ATR inhibitor ceralasertib.

In the second group, low ctDNA levels before treatment were linked to longer progression-free survival — 10.2 months versus 4.4 months for patients with higher ctDNA levels. Tumour response rates were 40% for those with low ctDNA compared with 9.7% for those with higher levels.

In the first group, a weaker association was observed before treatment, but after four weeks, patients with undetectable ctDNA had their cancer kept at bay for 10.6 months, compared with 3.5 months for those with detectable ctDNA. Similar results were observed in the second group, where ctDNA disappearance after four weeks corresponded with 12 months of progression-free survival, compared with 4.3 months in patients with detectable ctDNA.

“By analysing circulating tumour DNA in blood samples from patients with advanced breast cancer, we identified a clear link between these levels, both at the start and after one cycle of treatment, and how well patients responded to therapy,” Browne said. “These findings support the use of ctDNA as a non-invasive biomarker for predicting outcomes and monitoring treatment response.”

Prof. Nicholas Turner, a professor of molecular oncology at the ICR and consultant medical oncologist at the Royal Marsden, added: “This research looked at advanced breast cancer, but these tests could also work for early-stage breast cancers. The liquid biopsy has the potential to make treatment decisions faster, more personalised, and ultimately more effective.”