ESR1 and breast carcinoma: In 2020, 2 million new cases of BC were diagnosis in women globally.[1] In addition, the incidence of BC is increasing by 0.5% every year.[2] BC is a multifaceted disease characterized by a myriad of molecular and pathological diversities, leading to varied prognosis and therapeutic responses.[3] Previous study suggested that breast cancer were divided into 4 molecular subtypes based on estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2) and cell proliferation marker Ki-67.