ESR1 and breast carcinoma: Currently, salvage therapy for breast cancer patients includes fulvestrant (selective ER downregulators) [1, 2], cyclin-dependent kinase 4/6 inhibitors [3], aromatase inhibitors combined with everolimus (a mammalian analog of rapamycin which acts as a mammalian target of rapamycin (mTOR) inhibitor) [4], and histone deacetylase (HDAC) inhibitors [5].