Defects in the function of mismatch repair (MMR) genes result in genetic instability, a common feature of malignant progression. This study was conducted to determine the frequency of genetic instability [defined as microsatellite instability (MSI)] and to evaluate the sensitivity/specificity of immunohistochemistry in predicting the deficiency in MMR genes in renal cortical tumors. A total of 51 surgically-resected renal tumors (27 clear cell, 10 papillary, 5 chromophobe carcinomas and 9 oncocytomas) were studied. We also analyzed the correlation with clinicopathological parameters, the MSI status (assessed by using 5 microsatellite markers: D2S123, D11S904, D3S1621, D3S1683 and BAT26), and the immunohistochemical expression of 2 major MMR genes [the human mutL homolog 1 (hMLH1) and the human mutS homolog 2 (hMSH2)]. Sixteen cases (31.4%) showed MSI: Three (5.9%) demonstrated a high level of MSI, 11 (21.6%) demonstrated a low level of MSI, 2 (3.9%) presented with a loss of heterozygosity, and the remaining 35 (68.6%) exhibited microsatellite stability. The loss of hMLH1 and hMSH2 immunohistochemical expressions was observed in 5/51 (9.8%) and 9/51 (17.6%) cases, respectively. The complete absence of both hMLH1 and hMSH2 immunohistochemical expressions was observed only in the 3 cases with a high level of MSI. This study showed that defects in MMR genes are involved in renal carcinogenesis and correlate with the occurrence of MSI.

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