The extracellular matrix component periostin is a secreted protein that functions as both a cell attachment protein and an autocrine or paracrine factor that signals through the cell adhesion molecule integrins αvβ3 and αvβ5. Periostin participates in normal physiological activities such as cardiac development, but is also involved in pathophysiological processes in vascular diseases, wound repair, bone formation, and tumor development. It is of increasing interest in tumor biology because it is frequently overexpressed in a variety of epithelial carcinomas and is functionally involved in multiple steps of metastasis progression. These include the maintenance of stemness, niche formation, EMT, the survival of tumor cells, and angiogenesis, all of which are indispensable for gastric cancer metastasis. Periostin has been reported to activate the PI-3K/AKT, Wnt, and FAK-mediated signaling pathways to promote metastasis. Therefore, periostin represents a potentially promising candidate for the inhibition of metastasis. In this review article, we summarize recent advances in knowledge concerning periostin, its antagonist PNDA-3, and their influence on such key processes in cancer metastasis as maintenance of stemness, niche formation, epithelial-to-mesenchymal transition, tumor cell survival, and angiogenesis. In particular, we focus our attention on the role of periostin in gastric cancer metastasis, speculate as to the usefulness of periostin as a therapeutic and diagnostic target for gastric cancer metastasis, and consider potential avenues for future research.

AIMTo investigate the association between serum human epidermal growth factor receptor 2 (HER2) extracellular domain (ECD) and tissue HER2 status, and the prognostic value of serum HER2 ECD in patients with gastric cancer.METHODSA total of 239 patients with gastric cancer were enrolled from December 2012 to June 2013. Serum HER2 ECD was determined by chemiluminescent assay, and tissue HER2 status was evaluated by immunohistochemistry and fluorescence in situ hybridization assay. A receiver operating characteristic (ROC) curve was plotted to identify the optimal cut-off value for serum HER2 ECD assay for predicting survival in gastric cancer patients.RESULTSSerum HER2 ECD was significantly correlated with tissue HER2 status (P < 0.001), tumor size (P < 0.001), and intestinal type of gastric cancer (P = 0.021). Serum HER2 ECD levels differed significantly between patients with HER2-positive tissue expression and those with HER2-negative tissue expression. ROC analysis yielded an area under the curve value of 0.79 (95%CI: 0.71-0.87, P < 0.001), with a sensitivity and specificity of 0.54 (95%CI: 0.37-0.70) and 0.93 (95%CI: 0.88-0.96), respectively. With a cut-off value of 24.75 ng/mL, high serum HER2 ECD had a negative impact on overall survival of the patients (HR: 1.93, 95%CI: 1.32-4.38, P = 0.006).CONCLUSIONSerum HER2 ECD could be a highly specific surrogate biomarker for tissue HER2 status in gastric cancer. Optimal cut-off criteria for predicting survival should be established.