However, our panel includes the most frequently described clonal mutations in metastatic breast cancer such as PIK3CA and TP53 as well as other genes that have been linked to resistance to endocrine and targeted therapy in ER + /HER2− breast cancer such as ESR1, ERBB2, FGFR1, PTEN, AKT117,18. Here, ERBB2 is linked to breast cancer.