A Randomized Secondary Adjuvant Treatment Intervention Study Comparing Trastuzumab-Deruxtecan to SOC Therapy in eBC Patients With Molecular Relapse

This trial is testing whether starting the antibody-drug conjugate trastuzumab deruxtecan (T-DXd) early — when a sensitive blood test detects signs of cancer returning but before it is visible on scans — can prevent or delay full metastatic relapse in people with HER2-positive or HER2-low early breast cancer. **You may be eligible if...** - You are between 18 and 75 years old - You have HER2-positive or HER2-low breast cancer that was treated with curative intent (surgery, chemotherapy, radiation) - You are enrolled in the SURVIVE study and a liquid biopsy (ctDNA test) has shown signs of cancer returning - There is no visible metastatic disease on imaging - Your heart function, blood counts, and organ function meet required levels **You may NOT be eligible if...** - You have stage IV (metastatic) breast cancer - You have had prior treatment with trastuzumab deruxtecan (T-DXd) - You have significant heart problems (heart failure, recent heart attack) - You have a history of lung disease or pneumonitis requiring steroids - You have active HIV, uncontrolled hepatitis B or C - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.