ECLECTIC: EstroTEP and Circulating Biomarkers for ER-positive HER2-negative Metastatic Breast Cancer Patients

This study uses a special type of PET scan (EstroTEP) along with blood biomarkers to predict which patients with hormone receptor-positive (ER+), HER2-negative metastatic breast cancer will respond to hormone-blocking therapies. It aims to help doctors personalize treatment plans. **You may be eligible if...** - You are 18 or older (male or female) - You have metastatic invasive breast cancer that is estrogen receptor-positive (ER+) and HER2-negative - Your life expectancy is greater than 3 months - You are well enough to perform daily activities (ECOG 0–2) - A tumor tissue sample (biopsy block) is available **You may NOT be eligible if...** - Your breast cancer is HER2-positive or ER-negative - You have very poor overall health - You have no available tumor tissue for analysis Talk to your doctor to see if this trial is right for you.