Gentuximab

Primary objective: To compare the overall survival (OS) of patients with advanced gastric or GEJ adenocarcinoma who have failed first-line treatment with gintuximab injection combined with paclitaxel injection and placebo combined with paclitaxel injection. Secondary objectives: (1) To compare other efficacy indicators of patients with advanced gastric or GEJ adenocarcinoma who have failed first-line treatment with gintuximab injection combined with paclitaxel injection and placebo combined with paclitaxel injection. (2) To compare the safety characteristics of patients with advanced gastric or GEJ adenocarcinoma who have failed first-line treatment with gintuximab injection combined with paclitaxel injection and placebo combined with paclitaxel injection. (3) To evaluate the population pharmacokinetic (PPK) characteristics and immunogenicity of gintuximab injection/placebo in patients with advanced gastric or GEJ adenocarcinoma who have failed first-line treatment. (4) To compare the quality of life of patients with advanced gastric or GEJ adenocarcinoma who have failed first-line treatment with gintuximab injection combined with paclitaxel injection and placebo combined with paclitaxel injection.