JSKN003 Versus Trastuzumab Emtansine (T-DM1) for HER2-Positive, Advanced Breast Cancer

This study is comparing a new drug called JSKN003 to an existing standard treatment (trastuzumab emtansine, also known as T-DM1) in people with HER2-positive advanced breast cancer — a type of breast cancer driven by overexpression of a protein called HER2. **You may be eligible if...** - You are 18 or older with confirmed HER2-positive advanced or metastatic breast cancer - Your cancer is not surgically removable - You have already received a HER2-targeted treatment (like trastuzumab) and your cancer has since progressed **You may NOT be eligible if...** - You have previously received T-DM1 treatment - You have active brain metastases that are unstable - You have significant heart problems - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.