Abstract: BACKGROUND ＆ AIM： To explore the mechanism of Helicobacter Pylori (H.pylori)-related gastric carcinogenesis and overexpression of the multidrug-resistant-1 (MDR-1) gene-encoded P-glycoprotein (P-gp) via examining Cyclooxygenase-2(COX-2) and P-gp expression in the affected gastric mucosa. MATERIAL AND METHODS: 155 chronic gastritis specimens (30 chronic superficial gastritis specimens, 40 chronic atrophic gastritis specimens, 45 intestinal metaplasia specimens, 40 dysplasia specimens) and 80 gastric carcinoma specimens(40 intestinal type and 40 diffuse type) were selected. COX-2 and P-gp expression were detected by immunohistochemistry. H. pylori infection was assessed by rapid urease test and histological examination(modified Giemsa staining). RESULTS: H.pylori infection rate，COX-2 positive expression rate and P-gp positive expression rate in intestinal-type gastric carcinoma specimens were significantly higher than those in diffuse-type gastric carcinoma specimens(P<0.01). Expression of COX-2 was positively correlated with H.pylori infection in chronic atrophic gastritis, intestinal metaplasia, dysplasia and intestinal-type gastric carcinoma(P<0.01). Expression of COX-2 was positvely correlated with that of P-gp in chronic superficial gastritis，chronic atrophic gastritis, intestinal metaplasia, dysplasia，and intestinal-type gastric carcinoma with H.pylori infection (P<0.01). CONCLUSION: H. pylori-dependent induction of COX-2 was associated with enhanced prodution of P-gp that might contribute to gastric tumourigenesis and resistance to chemotherapy.

Key words: gastric carcinoma, helicobacter pylori, cyclooxygenase-2, P-glycoprotein