A simple blood test may soon help doctors decide which breast cancer treatment is most likely to work for each patient, according to a new study. Researchers say the test could allow patients to receive the most effective treatment earlier, while avoiding therapies that are unlikely to help.
Breast cancer is the most common cancer worldwide, with more than two million people diagnosed each year. While treatment options have improved significantly, doctors still face a major challenge: predicting which treatment will work best for an individual patient. At present, many patients must try a therapy first and wait to see if it works, losing valuable time if it does not.
Scientists at the Institute of Cancer Research (ICR) have developed a new type of liquid biopsy, a DNA blood test, that may change this. The test analyses circulating tumour DNA (ctDNA), which are tiny fragments of cancer DNA released into the bloodstream by tumour cells. By measuring ctDNA levels, doctors can assess how a patient’s cancer is likely to respond to treatment, even before therapy begins.
The study involved 167 patients with advanced breast cancer. Blood samples were taken before treatment started and again after four weeks, following one cycle of therapy. Researchers found a strong link between low ctDNA levels and better treatment outcomes. Patients with lower ctDNA levels at baseline or whose ctDNA became undetectable after 4 weeks responded significantly better to treatment.
Dr Iseult Browne, the study’s first author, said the findings show how powerful this simple test could be. She explained that early knowledge of whether a treatment is working allows doctors to switch strategies quickly. Patients could be moved to alternative targeted therapies, combination treatments, or even clinical trials before their cancer has a chance to progress.
The study included two patient groups. One group had breast cancers with specific genetic mutations and received targeted treatments matched to those mutations. The second group had triple-negative breast cancer, an aggressive form of the disease that accounts for around 10–15% of cases globally and has fewer treatment options. In this group, patients with low ctDNA levels before treatment had better outcomes, including longer periods without worsening of the cancer.
Even after just four weeks of treatment, ctDNA levels remained a strong predictor of success in both groups. Patients whose ctDNA became undetectable experienced significantly longer periods of disease control than those whose ctDNA remained detectable.
Professor Nicholas Turner, a consultant oncologist at the Royal Marsden, said the test has the potential to make cancer treatment faster, more personalised, and more effective. While the current research focused on advanced breast cancer, he added that similar tests could also prove useful for early-stage disease.
Funded by organisations including Breast Cancer Now and Cancer Research UK, the study highlights how a simple blood test could transform breast cancer care, helping patients receive the right treatment at the right time and improving their chances of living longer, healthier lives.
