Loss of PCDH9 is associated with the differentiation of tumor cells and metastasis and predicts poor survival in gastric cancer.

Microarray studies revealed down-regulation of PCDH9 mRNA level in lymph node metastasis of gastric cancer compared with the primary tumors. The expression of PCDH9 protein and its clinicopathological relevance were assessed on tissue microarrays of 1072 cases of gastric cancer. Its prognostic value was further evaluated on a small cohort of 175 gastric cancers. PCDH9 was down-regulated during the development and progression of gastric cancer. The overall rates of PCDH9 expression in normal, primary tumor, nodal and hepatic metastatic tissues were 100 % (1072/1072), 48.0 % (515/1072), 20.1 % (34/169), and 5.6 % (1/18), respectively. Positive staining of PCDH9 protein was significantly reversely correlated with tumor size, tumor differentiation, tumor invasion, lymph node metastasis, and disease progression. The Cox proportional hazards model revealed that the PCDH9 was an independent prognostic factor for gastric cancer. Therefore, decreased expression of PCDH9 is frequent in human gastric cancer metastasis and PCDH9 expression is an independent prognostic factor, suggesting that PCDH9 could be a promising biomarker of this malignancy.