Breast cancer is a heterogeneous disease based on the expression of the estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor-2 (HER2), which can be divided into five entirely different subtypes, including luminal A, luminal B, Her-2 overexpressed, normal breast-like and triple-negative breast cancer (TNBC) [4, 5]. Here, ESR1 is linked to breast cancer.