This study aims to assess the impact of adding olanzapine to nutritional advice and standard anti-tumor therapy on the survival and safety of patients with locally advanced, unresectable or metastatic gastric cancer, esophageal cancer, hepato-pancreaticobiliary cancer, and lung cancer. Researchers seek to determine whether olanzapine can improve progression-free survival (PFS), overall survival (OS), and objective response rate (ORR) in advanced cancer patients who received standard anti-tumor therapy, and investigate the relationship between olanzapine-induced weight changes and patient survival.