ObjectiveTo analyze the difference of expression of B7 superfamily member 1 (B7S1) in gastric cancer and adjacent cancer tissues, and to explore the relationship between B7S1 expression and the clinicopathological characteristics and the prognosis of gastric cancer patients.MethodsReverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry were performed to investigate the expression of B7S1 in 78 cases of gastric cancer tissues and adjacent tissues. The correlation of B7S1 expressions with the clinicopathological characteristics and prognosis of the patients was analyzed.ResultsThe results showed that cancer tissues relative expression of B7S1 mRNA was higher than that of adjacent tissues, and the difference was statistically significant (P<0.05). The results showed that positive rate of B7S1 protein expression in gastric cancer tissues was significantly higher than that of adjacent tissues, 74.36% and 11.54%, the difference was statistically significant (P=0.001). Chi-square analysis showed that the expression of B7S1 protein was associated with tumor diameter (P=0.006), pathological-stage (P=0.002), T-stage (P=0.011), and lymph node metastasis (P=0.001). There were no relationship with gender, age, tumor site, and M-stage (P>0.05). B7S1 protein expression was correlated with the overall survival rate for gastric cancer patients. Both univariate and Cox multivariate survival analysis suggested that B7S1 positive expression was a risk factor for poor prognosis in patients with gastric cancer.ConclusionsThe relative expression level of B7S1 mRNA and the positive rate of protein expression in gastric cancer tissues are higher than those in adjacent tissues. The positive expression of B7S1 is correlated with the poor clinicopathological characteristics and prognosis. We speculate that B7S1 may be involved in the malignant progression of gastric cancer.