Objective  To investigate the expression and significance of Claudin 3 in adenocarcinoma of esophagus and gastric cardia.   Methods  We subjected pathologically confirmed 16 cases of esophageal adenocarcinoma (EAC)

20 cases of esophageal squamous cell carcinoma (ESC)

and 40 cases of gastric cardiac adenocarcinoma (CAC

including 15 diffuse and 25 intestinal cases). Tissue samples were collected with aid of gastroscope. Fifteen samples of normal esophageal mucosa and 15 samples of normal cardiac mucosa served as control. RT-PCR and Western blotting were used respectively to detect the mRNA and protein expression of Claudin 3 in these tissue samples.   Results  The mRNA and protein expressions of Claudin 3 were increased in EAC and intestinal CA compared with those in normal tissues

ESC and diffuse CAC. There was no significant difference of the expression of Claudin 3 between normal group and ESC and diffuse CAC group.   Conclusion  Claudin 3 might be related to the development of EAC and intestinal CAC

and expected to be the tumor maker and therapeutic target of this kind of carcinoma.