Expression of hMSH2 and hMLH1 proteins of the human DNA mismatch repair system in salivary gland tumors

Background:  The human DNA mismatch repair (hMMR) system plays an important role in reducing mutation and maintaining genomic stability. The MMR system in human cells is composed of at least six genes (hMSH2, hMLH1, hMSH3, hPMS1, hPMS2 and GTBP/hMSH6). In particular, hMSH2 and hMLH1 are expressed in cells undergoing rapid renewal; their reduced expression has been reported in several tumors. Methods:  We examined the expression of hMSH2 and hMLH1 by immunohistochemistry in tumor specimens from 43 patients with primary tumors. Results:  All carcinomas (n = 20) expressed these proteins. In addition, when compared to pleomorphic adenomas, malignant tumors contained significantly (P < 0.01) higher proportions of hMSH2 (56.1 ± 31.5 vs. 31.1 ± 22.6) and hMLH1 (27.9 ± 26.0 vs. 14.0 ± 12.6) positive cells. Warthin's tumors showed no specific nuclear staining of tumor cells for both hMSH2 and hMLH1. Conclusions:  These data suggest a minor, if any, role for a defect in the hMMR system in the pathogenesis of malignant salivary gland tumors.