Among these genes, we further selected six GI hormone receptors whose expression was significantly down-regulated by 80–100% in the primary gastric tumors, including neuropeptide Y receptors (NPY1R and PPYR1), prostanoid receptors (PTGDR, PTGER2, and PTGER3), and a somatostatin receptor (SSTR2) (Fig. 4b). The gene discussed is PTGDR; the disease is gastric neoplasm.