Utilizing Liquid Biopsy for Treatment Management in Bone Dominant Metastatic Breast Cancer

Applications of liquid biopsy are primarily to monitor treatment response and to detect secondary treatment resistant mutations. In patients with bone-dominant metastatic breast cancer it can be challenging to evaluate for new mutations. Here, we present two patient cases with bone-dominant hormone positive metastatic breast cancer in whom we utilized liquid biopsy testing to guide therapy upon disease progression. Liquid biopsies were used to evaluate circulating-tumor DNA and analyzed for mutations using next generation sequencing. PIK3CA mutations were identified in both cases allowing the use of FDA approved PIK3CA-directed treatment with alpelisib. These cases demonstrate the clinical use of liquid biopsy in identifying actionable mutations, offering patients targeted treatment options without undergoing a metastatic biopsy. More real world reports are needed to further understand current liquid biopsy utilization in oncology patient care.