ESR1 and breast carcinoma: More recently, high-throughput technologies studies in ER-positive metastatic breast cancer samples have identified a large number of molecular aberrations in potential driver genes such as PIK3CA mutations, FGFR1 and CCND1 amplifications (11 %), and ESR1 mutations (4 %) [12, 15–19], some of them previously linked to endocrine resistance.