ESR1 and breast neoplasm: More recently, deep sequencing of 929 breast tumor biopsies (including ER-positive, HER2-positive and ER-negative tumors) indicated 95 patients (10.2%) having somatic mutations in ESR1, which consisted of 20 (21.1%) of E380Q, 34 (35.8%) of D538G in comparison with 13 (13.7%) of Y537S, 6 (6.3%) of Y537C, and 5 (5.3%) of Y537N [24].