🧠 TL;DR Trastuzumab Deruxtecan is a HER2-targeted antibody-drug conjugate (ADC) Combines targeting + chemotherapy in one molecule Used in HER2-positive and HER2-low breast cancer, gastric & some lung cancers Given once every 3 weeks (half-life ~6 days) ❌ NOT the same as trastuzumab (Herceptin) or T-DM1 → common dangerous confusion ⚠️ Major risks: lung toxicity (ILD), heart dysfunction, bone marrow suppression 💰 Cost varies widely → depends on weight, schemes & support progr