ESR1 and breast cancer: Approximately 15% of breast cancers are triple negative, in which the tumor lacksexpression of estrogen receptor (ER), progesterone receptor (PR), and humanepidermal growth factor receptor 2 (HER2).1 However, the representation of triple-negative subgroup is much higher inthose that recur or metastasize (5-year overall survival is 77% for triple negativevs >90% for others).