The SERENA-6 trial in HR-positive, HER2-negative advanced or metastatic breast cancer signals a potentially important shift in precision oncology, using ctDNA to identify molecular resistance and guide treatment changes before radiographic progression.

This insight brief explores how lessons from SERENA-6 could reshape definitions of cancer progression and treatment lines, influence clinical trial design and endpoints, and inform oncology drug development as treatment becomes increasingly molecularly guided and biologically adaptive.