Researchers presented new data at ESTRO 2026 on a blood-based circulating tumor DNA approach for tailoring treatment in oligometastatic breast cancer. The work uses ctDNA detected in plasma as a biomarker to inform therapeutic decisions, positioning the assay as a potential decision layer before or around radiotherapy. The report ties the ctDNA readout to treatment selection for patients whose disease has begun to spread but remains limited—an area where clinicians increasingly want earlier signals of biology and response. Details on performance metrics were not provided in the excerpt, but the presentation frames ctDNA as a practical, minimally invasive tool to guide therapy in advanced settings where treatment selection is challenging.