ESR1 and breast cancer: Recent findings from an international multicenter randomized trial demonstrated that the SUV values from [18F]FES PET/CT in metastatic ER+HER2- breast cancer patients can identify distinct subgroups: those with endocrine-resistant disease who are likely to benefit from chemotherapy and those with endocrine-sensitive tumors for whom endocrine therapy alone is linked to exceptionally prolonged survival [28,29].