The purpose of study is to evaluate the efficacy and safety of postoperative adjuvant
chemotherapy with Nivolumab in combination with tegafur-gimeracil-oteracil potassium (S-1
therapy) or capecitabine + oxaliplatin (CapeOX therapy), in comparison with placebo in
combination with S-1 therapy or CapeOX therapy, in pStage III gastric cancer (including
esophagogastric junction cancer) after D2 or more extensive lymph node dissection.