Objective    To study the expression of Claudin-3 in gastric adenocarcinoma tissue and its relation with the prognosis.     Methods    Expression of Claudin-3 was detected in normal gastric epithelium

gastric epithelium with intestinal metaplasia

mucosa layer

central area of tumor

invasive front area and lymph node metastasis of 139 patients with gastric adenocarcinoma by tissue microarray and immunohistochemistry

respectively. Relation between the location and expression of Claudin-3 in gastric adenocarcinoma

and the clini-copathological features

invasive metastasis

prognosis of gastric adenocarcinoma

were analyzed.     Results    The moderate-strong expression rate of Claudin-3 was significantly higher in gastric epithelium with intestinal metaplasia than in normal gastric epithelium (100.0% vs 17.5%

chi-square=78.12，P0.05）. The expression of Claudin-3 in gastric cancer tissue showed two staining patterns. Claudin-3 was located in membranes of intestinal gastric adenocarcinoma cells

in cytoplasm of diffuse gastric adenocarcinoma

and in both membranes and cytoplasm of mixed gastric adenocarcinoma. The moderate-strong expression rate of Claudin-3 with membranous staining and weak cytoplasm staining

and mixed membrane and cytoplasm staining in mucosa layer

central area of tumor

invasive front area and lymph node metastasis was 59.4%（61/88）

85.3% (75/88)，36.4% (32/88)，and 23.9% (21/88)

respectively

which increased at first and then decreased. The expression level of Claudin-3 was the highest in central area of tumor and the lowest in lymphatic metastasis (chi-square=110.83，P0.05). The moderate-strong expression rate of Claudin-3 with cytoplasm staining was 11.8%（6/51）

33.3% (17/51)，51.0% (26/51)，and 15.7% (8/51)

respectively

and was the highest in invasive front area (chi-square=31.32

P0.05). The median survival time of gastric carcinoma patients with overexpression of Claudin-3 in membrane of gastric mucosa cells was longer than those with weak expression of Claudin-3 (chi-square=9.36，P0.05).     Conclusion    Expression of Claudin-3 in gastric adenocarcinoma may be related with the histological typing of gastric cancer cells. Claudin-3 is heterogenetically expressed in different sites of invasive gastric metastasis. Expression of Claudin-3 in mucosa layer of gastric adenocarcinoma may be a potential prognostic marker for its prognosis.