ESR1 and cancer: Based on the molecular pathogenesis of these two cancer subtypes, multiple effective targeted therapies have been developed, such as endocrine agents for estrogen receptor (ER)-positive or progesterone receptor (PR)-positive breast cancers, anti-HER2 antibodies (such as trastuzumab and pertuzumab), and small-molecule tyrosine kinase inhibitors (such as lapatinib and neratinib) for HER2-positive types4.