The disruption of tight junction protein expression in cancer might account for invasiveness, loss of cohesion, and lack of differentiation. Our cDNA array data indicated that claudin 7 was up-regulated in gastric carcinoma. We investigated the expression patterns and clinical implications of claudin 7 in gastric cancer. By immunohistochemical staining and Western blot, claudin 7 was significantly more often expressed in intestinal metaplasia, adenoma and cancer than in normal gastric epithelium. Twenty-seven (47.4%) of 57 normal gastric epithelium samples did not express claudin 7, but 50 (86.2%) of 58 intestinal metaplasia, 11 (91.7%) of 12 adenoma tissues, and 129 (82.7%) of 156 cancer samples did. Claudin 7 was more often unexpressed in diffuse type gastric cancer than in intestinal type. Only 13 (11.2%) of 116 intestinal type samples did not express claudin 7, but 14 (41.2%) of 34 diffuse type samples showed no expression. Compared to normal gastric epithelium, intestinal type gastric cancer significantly more often expressed claudin 7, but diffuse type did not. The expression pattern of claudin 7 did not change as cancer progressed. In this study we show that claudin 7 expression changed with the gastric carcinogenic process and that this is implicated in cancer characteristics.

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