Positron Emission Tomography (PET) Imaging With Zirconium-89 (89Zr)-Trastuzumab for Prediction of HER2 Targeted Therapy Effectiveness

This study is using a special type of PET scan (a whole-body imaging scan using a tracer attached to a breast cancer drug) to predict whether HER2-positive breast cancer patients — those whose tumors have a protein called HER2 that drives growth — will respond to targeted treatment before starting therapy. **You may be eligible if...** - You are 18 or older - You have been diagnosed with HER2-positive breast cancer (confirmed by lab testing) - You are about to start or are currently receiving HER2-targeted therapy - You are willing to undergo the special PET scan **You may NOT be eligible if...** - Your cancer is not HER2-positive - You are pregnant or breastfeeding - You have conditions that make the scan or tracer unsafe - You have had certain previous treatments that would interfere with results Talk to your doctor to see if this trial is right for you.