This study aims to evaluate whether ^68Ga-TROP2 PET/CT, combined with ^18F-FDG PET/CT, can predict the efficacy of anti-TROP2 antibody-drug conjugates in patients with advanced HER2-negative breast cancer. Baseline and dynamic imaging parameters will be used to develop prediction models (primary endpoint: AUC), and their associations with clinical outcomes and tumor TROP2 status will be explored.

Inclusion Criteria:

• Patients diagnosed with advanced/metastatic HER2-negative breast cancer with confirmed metastatic disease, regardless of being de novo diagnosed or progressed from a non-metastatic stage.
• Patients who are planned to receive anti-TROP2 antibody-drug conjugate (ADC) therapy (e.g., sacituzumab govitecan or datopotamab deruxtecan) as part of routine clinical care.
• Patients who will undergo protocol-defined ^68Ga-TROP2 PET/CT and ^18F-FDG PET/CT during the study (baseline imaging, with repeat imaging per protocol if applicable).
• Adult patients (≥18 years) who are able to provide informed consent and comply with study procedures.

Exclusion Criteria:

• Patients with incomplete medical records or inability to complete the required imaging assessments.
• Patients with prior exposure to an anti-TROP2 ADC.
• Patients with known contraindications to PET/CT or known allergy to ^18F-FDG or the ^68Ga-TROP2 tracer (or their components).
• Patients who are pregnant or breastfeeding.
• Patients diagnosed with secondary primary tumors (other active malignancies), as determined by the investigator.