Background T-lymphoma and metastasis gene 1 (Tiam1) produces a guanine nucleotide exchange factor (GNEF) that regulates guanosine triphosphatase,which transforms guanosine diphosphate to guanosine triphosphate.Recently published data indicate that Tiam1 was associated with gastric cancer.The aim of this study was to investigate biological effects and potential mechanisms of Tiam1 in gastric carcinoma.Methods We analyzed the expression of Tiam1 in 114 pair-matched gastric neoplastic and adjacent non-neoplastic tissues by quantitative real-time PCR.We investigated Tiam1 expression and its prognostic value for gastric cancer.Furthermore,the functions of Tiam1 over-expression were analyzed with stable-expression Tiam1 plasmid in human gastric cancer cell lines.Results Tiam1 expression was significantly associated with cell differentiation and lymphatic metastasis; expression of Tiam1 mRNA was up-regulated in gastric cancer compared to pair-matched adjacent non-tumor tissues.Analyses of surgical tissue samples and 5-year survival of gastric cancer patients showed that those with strong Tiam1 expression had significantly shorter overall survival time than those with negative Tiam1 expression.Ectopic expression of Tiam1 promoted cell growth,migration and invasion of gastric cancer cells in vitro.Conclusions In gastric cancer cells,Tiam1 affects multiple properties associated with acquisition of the metastatic phenotype,and may be a marker ofgastric cancer progression and metastasis in a subset of cancer.