Currently, [18F]FES is under investigation to optimize tamoxifen dosing (NCT04174352), guide therapy in ER-positive metastatic BCa (NCT05068726, NCT05486182), assess ER expression in metastases with ER-negative primary tumor (NCT06344767), and evaluate axillary lymph node metastasis in ER-positive BCa (NCT06695039). Here, ESR1 is linked to neoplasm.