HER2-PET as a Precision Imaging Tool for Treatment With HER2-ADC in HER2-expressing mBC

This study is using a special PET imaging scan that detects HER2 (a protein linked to cancer cell growth) to identify which patients with metastatic or advanced breast cancer are most likely to benefit from HER2-targeted antibody-drug conjugate therapy. The goal is to make cancer treatment more precise by matching patients to the right therapy based on their tumor's HER2 activity. **You may be eligible if...** - You are a woman aged 18 or older - You have metastatic or locally advanced breast cancer that has progressed after at least one line of chemotherapy, or has relapsed within 6 months after completing adjuvant chemotherapy - You have at least one metastatic lesion of 10 mm or larger that can be biopsied (or have a recent biopsy available) - You are willing and able to give written consent **You may NOT be eligible if...** - Your breast cancer lesions are too small or inaccessible for biopsy - You have had prior treatment with the HER2-targeting therapies being tested in this study - You have serious organ problems that would make treatment or imaging unsafe - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.