ESR1 Testing in the Era of Precision Oncology: A Mini Review

Estrogen receptor alpha, encoded by the ESR1 gene, is a major oncogenic driver in hormone receptor-positive/HER2-negative breast cancers. While endocrine therapies are effective in treating this subgroup, patients with advanced or metastatic disease may develop resistance associated with acquired somatic ESR1 mutations. This mini review summarizes recent clinical and technological advances in understanding ESR1 mutations, newly approved targeted therapies, and the use of liquid biopsy companion diagnostics, with a focus on their implications for pathologists.