Defects in mismatch repair genes, particularly the hMLH1 and hMSH2 genes, are associated with pathogenesis and prognosis of some cancers. The lack of correlation between replication error phenotype and mutations in hMLH1 in sporadic human cancers suggested that inactivation of the hMLH1 gene may be associated with promoter hypermethylation. This study was to investigate the association of hMLH1 promoter hypermethylation and hMLH1 protein expression in oral cancer. Our results indicated that all 75 cases (100%) were without any methylation of hMLH1 promoter by use of methylation-specific PCR (MSP). Nineteen of 99 cases (19.2%) were partial methylation by HpaII-based PCR. In addition, 24 (26.1%) of 92 cases of OSCC had reduced levels of hMLH1 protein. The concordance analysis showed that the expression level of hMLH1 protein was not correlated with methylation of hMLH1 promoter. Furthermore, the prognosis significance of hMLH1 or hMSH2 proteins on OSCC was also investigated. We analyzed the association of hMLH1 and hMSH2 protein expression with clinicopathological data of 92 cases of OSCC at KSVGH. We found that 24 (26.1%) of 92 cases of OSCC had reduced levels of hMLH1 protein, however only 10 cases (10.9%) had reduced hMSH2 by use of IHC. In addition, the reduced expression of hMLH1 correlated with the tumor differentiation and N classification. However, none of these clinical and pathological characteristics of the OSCC patients were associated with the extent of hMSH2 expression. Finally, previous studies reports that the hMLH1 and Aurora-A are directly involved in the prognosis of several cancers. The expression levels of hMLH1 and Aurora-A protein were investigated in the 138 tumor samples for consecutive patients with pathological confirmed primary buccal carcinoma (BC). Then the association of the protein expression with clinicopathological data and survival were also evaluated. The loss of hMLH1 protein was found in 15 (10.9%) of 138 tumor sections by IHC. In addition, loss of hMLH1 protein expression was not any correlated with clinical features and patients¡¦ prognosis. The up-regulation of Aurora-A protein was found in 118 (85.5%) of 138 tumor sections by IHC. In addition, the up-regulation of Aurora-A protein expression was correlated with the pathological stage and T classification, but Aurora-A protein up-regulation was not correlated with prognosis. In conclusion, promoter methylation of hMLH1 might not play a potent role in the gene expression in oral cancer. Defective expression of hMLH1 but not hMSH2 was associated with the development of OSCC. In addition, the Aurora-A protein expression but not hMLH1 may affect the malignant behavior of BC. However, the hMLH1 and Aurora-A protein expression might be not the prognostic factors for BC patients.

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