Defects in the DNA Mismatch Repair System Do Not Contribute to the Development of Childhood Wilms Tumors

Wilms tumor is the most common childhood renal malignancy. Most Wilms tumors occur sporadically, whereas a genetic predisposition is described in 9-19% of the Wilms tumor patients. In addition to constitutional aberrations, somatic aberrations in multiple genetic loci such as WT1, WT2 or locus 11p15.5, CTNNB1, WTX, TP53, FBXW7, and MYCN have also been linked to Wilms tumorigenesis. In sporadic Wilms tumors, however, the driving somatic genetic aberrations need to be further unraveled. Therefore, it is necessary to obtain more insight into other underlying mechanisms. Little is known about the role of defects in the DNA mismatch repair system in the etiology of Wilms tumors. To detect mismatch repair deficiency in a full cohort of Wilms tumor patients, we combined immunohistochemistry for the expression of mismatch repair proteins and microsatellite instability (MSI) analysis by a fluorescent multiplex polymerase chain reaction-based assay. Of the 121 Wilms tumor patients treated between 1987 and 2010 in our institution, 100 samples from 97 patients were available for analysis. Nuclear staining for MLH1, MSH2, MSH6, and PMS2 proteins was present in all 100 Wilms tumor samples. No pattern of MSI was found in any of the 100 investigated Wilms tumor samples. The matching results of normal expression of the mismatch repair proteins detected by immunohistochemistry and the absence of MSI by DNA analysis in 100 Wilms tumor samples lead us to conclude that defects in the DNA mismatch repair system do not play a significant role in the development of Wilms tumors.