We further designed methylation-specific PCR assays to assess the methylation status of PTPRD promoter CpG island in primary GC tissues. Taken together, our research suggested that PTPRD was a candidate tumor suppressor in GC. Low expression of PTPRD was a reliable indicator of disease progression and poor prognosis of GC. Receptor protein Ibrutinib 936563-96-1 tyrosine phosphatase delta is a member of the highly conserved family of receptor protein tyrosine phosphatases. The PTPs are a superfamily of enzymes that function in a coordinated manner with protein tyrosine kinases to control signalling pathways that underlie a broad spectrum of fundamental physiological processes. These enzymes are divided into the classical group, phosphotyrosine -specific phosphatases and the dual specificity phosphatases. There are 107 PTPs encoded in the human genome, of which 38 belong to the group of classical PTPs, which show specificity for phosphotyrosine. PTPs are signaling molecules that regulate a variety of cellular processes, including cell growth, differentiation, mitotic cycle and oncogenic transformation. Recently, several classical PTPs have been identified as potential tumor suppressors, including receptor PTPs such as DEP1, PTPk and PTPr. This group of genes is increasingly thought to be important in cancer development and progression. The PTPRD gene is located at chromosome 9p23–24.1, an area of human genome that is frequently lost in many kinds of tumors. Urushibara et al. described a selective reduction in PTPRD expression in hepatomas and first proposed PTPRD as a tumor suppressor. Subsequent studies reported homozygous deletions of PTPRD in a broad spectrum of human tumor types, such as lung adenocarcinoma, pancreatic carcinoma, melanoma and glioblastoma, etc. Kohno et al. observed reduced PTPRD expression in the majority of cell lines and surgical specimens of lung cancer. Veeriah et al. found that PTPRD was mutated in 6% of glioblastoma multiformes, 13% of head and neck squamous cell carcinomas, and in 9% of lung cancers. Their study revealed that loss of expression of PTPRD predicts for poor prognosis in glioma patients. These studies have established that PTPRD has a growth suppressive role in many types of human cancer. However, thus far, the expression, clinical significance and biological functions of PTPRD in gastric adenocarcinoma have not been explored. In our present study, we detected the mRNA and protein levels of PTPRD in GC patients by western blotting and qRT-PCR, respectively. PTPRD was expressed at both lower mRNA and protein levels in GC tissues compared with corresponding non-cancerous tissues. Moreover, immunohistochemistry showed decreased PTPRD expression in 261 out of 513 samples of gastric cancer patients. These results indicated that PTPRD might be a candidate tumour suppressor in GC. Our observation is in agreement with a series studies revealing that PTPRD expression is frequently lost or reduced in a number of human cancer tissues and cell lines, including lung cancer and glioblastoma multiforme. The correlation of PTPRD and clinical outcome was analyzed by immunohistochemical staining of specimens in large series of gastric cancer patients.