COX‐2 expression during 4‐nitroquinoline 1‐oxide induced rat tongue carcinogenesis

Abstract

ABSTRACT Background and aims: This study was undertaken to investigate, by immunohistochemistry, the expression of cyclooxygenase‐2 (COX‐2) during 4‐nitroquinoline 1‐oxide (4NQO)‐induced rat tongue carcinogenesis. Methods: Male Wistar rats were distributed into three groups of 10 animals each and treated with 50 ppm 4NQO solution through their drinking water for 4, 12, and 20 weeks. Ten animals were used as negative control. Results: Although no histopathological abnormalities were induced in the epithelium after 4 weeks of carcinogen exposure, COX‐2 was expresssed in some cells of the ‘normal’ oral epithelium in the superficial layer. In pre‐neoplastic lesions at 12 weeks following carcinogen exposure, the levels of COX‐2 were increased (P < 0.05) when compared to negative control. In well‐differentiated squamous cell carcinoma induced after 20 weeks of treatment with 4NQO, the same picture occurred when compared to negative control. Weak immunoreactivity for COX‐2 was observed in the negative control group being restricted to basal layer of the oral epithelium. Conclusions: Taken together, our results support the idea that expression of COX‐2 plays a crucial role during malignant transformation being closely related to neoplastic conversion of the oral mucosa cells.