Comparison Between ER Loss and Triple-Negative Breast Cancer Guided by 18F-FES PET/CT in Metastatic Breast Cancer

Inclusion Criteria: * Patients diagnosed with breast cancer (according to International Classification of Diseases 10th Revision) with confirmed metastasis, regardless of being de novo diagnosed or progressed from a non-metastatic stage. * MBC patients who underwent 18F-FES PET/CT at the Fudan University Shanghai Cancer Center between 2017 and 2023 * Patients diagnosed with primary ER-positive tumor and who were yet to receive any systemic therapy during the advanced stage * Contemporaneous patients with metastatic TNBC at initial diagnosis Exclusion Criteria: * Patients with incomplete medical records and those diagnosed with secondary primary tumors