ESR1 and neoplasm: Several molecular mechanisms, including loss or modification in ER expression, activation of estrogen‐independent signaling pathways, as well as a variety of factors that regulate epithelial–mesenchymal transition (EMT) in the tumor microenvironment, are reported to be associated to tamoxifen resistance in ER‐positive tumors (Mansouri, Farahmand, Hosseinzade, Eslami, & Majidzadeh, 2017; Mills et al., 2018; Ward et al., 2013; Zhang et al., 2018).