Abstract: Objective To study the role of the cyclooxygenase (COX)2 in the genesis of squamous cell by means of observation on its expression in oral leukoplakia, lichen planus and squamous cell carcinoma.Methods COX-2 expression was observed in 51 cases of OLK (15 OLK, 36 OLK with dysplasia), 34 cases of OLP ( 19 OLP, 15 OLP with dysplasia),52 cases of SCC and 10 cases of normal oral mucosa by immunohistochemistry. The number of positive cells was counted by image analysis system and COX-2 expression was analyzed by statistical method.Results The strong expression of COX-2 in the OLK was 6.7% (1/15); 50% (18/36) in the OLK with dysplasia; 15.8% (3/19) in the OLP; 33.3% (5/15) in the OLP with dysplasia; and 7.7% (4/52) in the SCC respectively. The positive rate was higher in the OLK with dysplasia than in the OLK or SCC (P<0.01). The higher positive rate was detected in the OLP with dysplasia than in the OLP or SCC (P<0.05). There were no significant differences between OLK, OLP and SCC (P>0.05).Conclusion COX-2 overexpression occurred in the early stage of oral carcinogenesis, it could be an important target for the chemical prevention and therapy.

Key words: COX-2, oral leukoplakia, oral lichen planus, squamous cell carcinoma