ESR1 and cancer: Molecular-targeted therapy for various cancers have been widely applied against identified targets such as cyclin-dependent kinases (CDKs), estrogen receptor (ER), BCR activator of RhoGEF and GTPase (BCR)– ABL protooncogene 1 nonreceptor tyrosine kinase (ABL), epidermal growth factor receptor (EGFR), human epidermal growth factor receptor-2 (HER2), and vascular endothelium growth factor receptor (VEGFR), using selective inhibitors such as imatinib, erlotinib, herceptin, gefitinib, erlotinib, afatinib, and dacomitinib [8,9,10,11].