JSKN003 Combined Treatment of HER2-positive Gastric Cancer

Inclusion Criteria: * Age≥18 years old. * Histologically or cytologically confirmed diagnosis of gastric cancer. * The first-line population enrolls participants with HER2-positive unresectable locally advanced or metastatic gastric cancer who had not received systemic treatment, and Perioperative population enrolls participants with HER2-positive resectable gastric cancer who had not received treatment. * HER2-positive (defined as IHC3+ or IHC 2+/FISH +). * The first-line population: presence of at least 1 measurable lesion per RECIST 1.1. Tumor lesions situated in a previously irradiated area are considered measurable if progression has been demonstrated in such lesions. * ECOG PS of 0 - 1. * Expected survival ≥ 3 months. * Participants with adequate organ functions. * Female and male patients of childbearing age agree to take adequate contraceptive measures during and upon completion of the study for 7 months after the last dose. Female participants of childbearing age must have a negative blood pregnancy test within 7 days before the first dose or randomization. * Voluntarily agree to participate in the study and sign the informed consent. Exclusion Criteria: * Has received anti-tumor treatment such as systemic chemotherapy or other trial interventions within 28 days, or immunotherapy (e.g. interleukin, interferon, thymospipeptide, etc.), hormone therapy or targeted therapy within 14 days or 5 half-life (whichever is shorter) before the first dose or randomization. * H…