Predicting Endocrine Resistance Using Molecular Imaging and Liquid Biopsy in Metastatic Breast Cancer

This prospective observational study aims to evaluate the prognostic value of molecular imaging biomarkers derived from baseline \[18F\]FES and \[18F\]FDG PET/CT for progression-free survival in patients with estrogen receptor (ER)-positive, HER2-negative metastatic breast cancer receiving first-line endocrine therapy combined with a CDK4/6 inhibitor. In a subset of patients with available tumor tissue, paired tumor tissue next-generation sequencing (NGS) and circulating tumor DNA (ctDNA) analysis will also be performed to investigate their associations with imaging biomarkers, treatment response, and clinical outcomes.