Abstract: BACKGROUND AND AIM: To investigate the expression of inducible nitric oxide synthase (iNOS) mRNA and its protein in Oral Squamous Cell Carcinoma (OSCC) and Precancerous Lesion(PL); in order to explore the impact of iNOS gene expression on the development of OSCC. MATERIALS AND METHODS: Immunohistochemistry technique (SABC) and in situ hybridization (ISH) assay were used to detect the expression of iNOS protein and iNOS mRNA in 10 specimens of normal oral mucosa,12 oral epithelial simple hyperplasia (SH),28 oral epithelial atypical hyperplasia (AH) and 32 OSCC. RESULTS: Both the expression of iNOS protein and mRNA were negative in the 10 normal oral mucosa.The positive rates in SH,AH and OSCC were 16.67％ 67.86％ and 78.13％ by SABC,16.67％、71.43％ and 75％ by ISH, respectively.No iNOS gene abnormality was found in OSCC by SABC and ISH.The positive rates of iNOS protein and iNOS mRNA were significant among these four groups of oral mucosa (P<0.01).Significant correlation between the expressions of iNOS protein and mRNA and the grade of atypical hyperplasia(AH) (P<0.05)was found. No significant difference of iNOS gene expression was found between AH and OSCC groups (P>0.05). CONCLUSION: The up_regulation of iNOS gene indicated that it may play important roles in the pathogenesis and development of OSCC. Determination of its gene products may provide evidence for early diagnosis.

Key words: oral squamous cell carcinorma, precancerous lesion, inducible nitric oxide synthase gene, in situ hybridization, immunohistochemistry