B7-H3 expression in gastric cancer: a novel molecular blood marker for detecting circulating tumor cells.

The clinical significance of B7-H3 expression in gastric cancer remains unclear, although the B7 ligand family plays a critical role in the T cell-mediated immune response. We therefore investigated B7-H3 expression as a blood marker of circulating tumor cells and determined correlations with tumor progression in patients with gastric cancer. B7-H3 expression in gastric cell lines was initially evaluated by immunocytochemistry. Furthermore, we used quantitative RT-PCR to assess B7-H3 mRNA expression in four cell lines and in 95 blood specimens from patients with gastric cancer, as well as in 21 samples of peripheral blood lymphocytes from healthy volunteers. B7-H3 expression in cell lines was identified by immunocytochemistry and quantitative RT-PCR. Blood specimens from patients with gastric cancer contained significantly more copies of B7-H3 mRNA than those from healthy volunteers without cancer (P < 0.0001). Levels of B7-H3 expression significantly correlated with overall stage (P = 0.013). The 5-year survival rate was significantly lower in patients with high B7-H3 expression than with low expression (P = 0.02). Multivariate analysis demonstrated that B7-H3 expression was an independent prognostic factor (P = 0.046). Our results indicate that B7-H3 appears to be a useful blood marker for predicting tumor progression in gastric cancer.