Phase 4 Study to Assess the Safety of Trastuzumab Deruxtecan, in Indian Patients

This is a post-marketing safety study for a drug called trastuzumab deruxtecan (T-DXd) — a targeted therapy for HER2-positive metastatic breast cancer — being conducted in India. It is monitoring how well the drug works and what side effects it causes in Indian patients in real-world clinical practice. **You may be eligible if...** - You are over 18 years old - You have metastatic or unresectable breast cancer that tests positive for HER2 (IHC 3+ or IHC 2+ with gene amplification confirmed) - You have received at least one prior HER2-targeted treatment - You are able to give informed consent **You may NOT be eligible if...** - You have previously been treated with trastuzumab deruxtecan (T-DXd) - You have significant heart disease, including recent heart attack, heart failure, or reduced heart pumping function (LVEF below 50%) - You have had or currently have serious lung inflammation (interstitial lung disease or pneumonitis) - You have active, uncontrolled infections or certain other serious medical conditions Talk to your doctor to see if this trial is right for you.