The accuracy of an individualized tumor response (ITR) assay in Japan was reportedly 74% (30th Annual Meeting of Japan Research Society for Appropriate Cancer Chemotherapy). Based upon the hypothesis according to which the appropriate adjuvant cancer chemotherapy will increase the survival outcome after surgery of advanced gastric cancer, we have clarified the usefulness of an ITR assay in evaluating the appropriate adjuvant chemotherapy for gastric cancer. While recent reports indicate the standard therapy for gastric cancer, the gastric cancer cohort includes responder and non-responder to adjuvant cancer chemotherapy. The ITR assay will be useful to differentiate the responder and nonresponder to cancer chemotherapy.