Detection of Tumor <i>PIK3CA</i> Status in Metastatic Breast Cancer Using Peripheral Blood

Analysis of plasma-derived ctDNA for the detection of PIK3CA mutations in patients with metastatic breast cancer is feasible. Our results suggest that PIK3CA mutational status can change upon disease recurrence, emphasizing the importance of reassessing PIK3CA status on contemporary (not archival) biospecimens. These results have implications for the development of predictive biomarkers of response to targeted therapies.