Imaging Versus Cardiac Biomarker Monitored HER2 Directed Therapy in Patients With Breast Cancer

This study compares two ways of monitoring the heart health of breast cancer patients receiving HER2-targeted therapy (a treatment for a specific subtype of breast cancer). One method uses regular cardiac imaging (scans), and the other uses blood tests (biomarkers). The goal is to find the safest and most efficient monitoring approach. **You may be eligible if...** - You have HER2-positive breast cancer that has not spread to other organs - You are scheduled to receive standard chemotherapy plus trastuzumab (with or without pertuzumab) - You are 18 or older - Your heart is in normal sinus rhythm and your heart function (LVEF) is above 55% - Your heart biomarker blood tests are within normal range **You may NOT be eligible if...** - You have contraindications to cardiac MRI - You have significant lung disease (COPD with reduced lung function) Talk to your doctor to see if this trial is right for you.