ESR1 and cancer: The prevalence of TP53 and PIK3CA gene mutations were similar to other studies,24-26 indicating that this panel is effective in identifying actionable mutations including PIK3CA mutations that indicate those patients who might benefit from treatment with PI3K inhibitors such as alpelisib.27 Our data show that variants in ESR1 and PIK3CA are identified in only a small proportion of HC and become much more prevalent in MBC, indicating the presence of these mutations arise because of the evolving cancer and not because of the benign pathology of a core biopsy.