ERBB2 and gastric cancer: This is a global, randomized, open-label study to compare the efficacy and safety of zanidatamab plus chemotherapy with or without the PD-1-blocking antibody tislelizumab with trastuzumab plus chemotherapy as a first-line treatment for patients with advanced HER2-positive (IHC 3+ or IHC 2+ with ISH positivity) gastric cancer.