IBI354 With or Without Pertuzumab Versus Taxane, Trastuzumab and Pertuzumab in HER2-positive Metastatic Breast Cancer

This study compares IBI354 (an antibody-drug conjugate — a targeted cancer drug with an attached chemotherapy payload) with or without pertuzumab versus a standard regimen of taxane chemotherapy plus trastuzumab and pertuzumab as a first-line treatment for HER2-positive metastatic breast cancer. **You may be eligible if...** - You are 18 or older with confirmed HER2-positive metastatic or locally advanced breast cancer that cannot be surgically removed - You have not received prior chemotherapy or HER2-targeted therapy for advanced or metastatic disease - Your overall health status is good (ECOG 0–1) - Your heart function, blood counts, liver, and kidneys are within acceptable ranges - You have at least one measurable tumor lesion **You may NOT be eligible if...** - You have previously received antibody-drug conjugates containing topoisomerase I inhibitors - You have uncontrolled heart disease, a recent heart attack, or a significant heart rhythm problem - You have a history of serious lung inflammation (interstitial lung disease) - You are pregnant or breastfeeding - You have active or uncontrolled infections Talk to your doctor to see if this trial is right for you.