ESR1 and breast cancer: ER-positive breast cancers have the most favorable prognosis among the four groups and typically respond to endocrine therapies, such as tamoxifen and aromatase inhibitors, or targeted endocrine-related therapies, such as PI3K-AKT-mTOR signaling, CDKs, epigenetic regulators and selective estrogen down-regulator (SERD)-selective estrogen receptor covalent antagonists31.