Immunocytochemical detection of hMSH2 and hMLH1 expression in oral SCC

BACKGROUND: The loss of DNA mismatch repair system was reported in hereditary non-poliposis colon cancer and in other tumours. The aim of this study was to detect the protein expression pattern of hMSH2 and hMLH1 in oral squamous cell carcinoma (SCC) by immunohistochemistry in paraffin-embedded tissues. MATERIALS AND METHODS: 5 specimens, obtained from healthy oral mucosa, and 20 from oral SCC were tested with anti-hMSH2 and anti-hMLH1 monoclonal antibodies. RESULTS: Six cases (30%) showed nuclear positivity in differentiated areas (G1) and cytoplasmic positivity in areas with a lower degree of differentiation, four cases (20%) showed only cytoplasmic positivity, and only one (5%) no staining. One case of oral SCC (5%) showed no hMLH1 staining in the tumoral cells, even if normal squamous epithelium available in this section showed a nuclear positivity; six cases (30%) showed nuclear positivity in differentiated areas (G1) and cytoplasmic positivity in areas with a lower degree of differentiation, three cases (15%) showed only cytoplasmic positivity. CONCLUSIONS: These data suggest that examination of hMSH2 and hMLH1 protein expression by immunohistochemistry is important in oral SCC. The analysis of mismatches expression in these cases of oral SCC might suggest that an absent nuclear staining for both hMSH2 and hML1 could constitute a hallmark of potential phenotype mutator for this type of neoplasia.