Diagnostic Accuracy and Safety Study of FES PET/CT in Assessment of ER Status of Recurrent or Metastatic Breast Cancer

\[18F\]FES PET/CT will be performed 90 min (± 10 min) after administration of \[18F\]FES. Patients will undergo core needle biopsy or surgery within 15 days after \[18F\]FES PET; or patients will undergo core needle biopsy within 30 days before \[18F\]FES PET. Experienced pathologists will determine metastatic/recurrent disease, and tumor histology including IHC. Patient will undergo surgery, radiation therapy or systemic therapy according to the results of staging workup, histology and biomarkers.