A significant UK study, conducted by a team at The Institute of Cancer Research (ICR), London, has demonstrated that a circulating tumour DNA (ctDNA) blood test can accurately predict how patients with advanced breast cancer will respond to targeted therapies. Published in the journal Clinical Cancer Research, these findings represent a crucial step towards more personalised and effective cancer treatment. The research involved analysing blood samples from 167 patients with advanced breast cancer enrolled in the plasmaMATCH trial. Researchers measured the levels of ctDNA, which are tiny fragments of cancer DNA released into the bloodstream by tumour cells. A strong correlation was observed between low or undetectable levels of ctDNA at the start of treatment, and after just one four-week cycle, and significantly better patient outcomes. Patients with low ctDNA levels experienced longer progression-free survival and higher response rates to therapy. For instance, some patients with undetectable ctDNA after four weeks saw their cancer kept at bay for 10.6 to 12 months, compared to 3.5 to 4.3 months for those with detectable ctDNA. This "liquid biopsy" approach offers a non-invasive method to monitor treatment effectiveness in real-time. It has the potential to allow clinicians to identify patients who are not responding well to their current treatment much sooner, enabling them to switch to alternative therapies more quickly and avoid ineffective drugs. This early intervention could significantly improve patient outcomes and quality of life. While the study focused on advanced breast cancer, researchers suggest that these tests could also be beneficial for early-stage breast cancers. The implications of this research are global. Breast cancer is a significant health concern in India, being the most common cancer among women, with many diagnoses occurring at advanced stages. The ability to personalise treatment based on such a test could be transformative for patient management in India and worldwide, reducing the burden of ineffective therapies and leading to better survival rates. Further validation in larger studies and integration into routine clinical practice are the next steps for this promising technology. The NHS in England is already rolling out similar liquid biopsy tests for lung and breast cancer patients, highlighting the growing clinical application of this technology.