The recent introduction of a new oral drug, S-1 (Shirasaka et al, 1996), which was developed on the basis of biochemical modulation to inhibit dihydropyrimidine dehydrogenase and orotate phosphoribosyltransferase to therapeutic modality for gastric cancer, has enabled us to increase ORR to 46–74% and MST to 10.9–14.8 months by its combination with cisplatin (CDDP), docetaxel or CTP-11, with less toxicity than 5-FU (Koizumi et al, 2003; Ajani et al, 2006; Inokuchi et al, 2006; Yamaguchi et al, 2006). Here, PSMD1 is linked to gastric cancer.