hMLH1 immunoexpression is related to the degree of epithelial dysplasia in oral leukoplakia

Background: hMLH1 is a protein of the mammalian mismatch repair system responsible for genomic stability during repeated duplication. Relation between its altered expression linked to microsatellite instability has also been observed in oral leukoplakias (OL) and squamous cell carcinomas pointing to a possible role of hMLH1 in oral carcinogenesis. To our knowledge, this is the first study evaluating the immunoexpression of hMLH1 in OLs regarding their different degrees of epithelial dysplasia. Methods: Sixty-two specimens of OL were classified in four groups: 17 without dysplasia, 19 with mild dysplasia, 16 with moderate dysplasia, and 10 with severe dysplasia. Immunohistochemistry for hMLH1 was performed, and percentage of positive cells was assessed. In the statistical analysis, P values < 0.005 were considered significant. Results: hMLH1 immunoexpression showed decreasing indexes from lesions with lower degrees of dysplasia to lesions with more severe dysplasia. Statistical difference was found mainly between suprabasal layers and total indexes. Conclusions: hMLH1 immunoexpression was inversely related to the OL degree of dysplasia. The total epithelial hMLH1 index seems to be of more clinical relevance than the evaluation stratified by layers. Our findings also suggest a role of such alterations in this pathway of DNA repair as an early event in oral carcinogenesis.