Alternative marker panel for microsatellite instability analysis in detection of constitutional MLH1 and MSH2 mutations.

Hereditary Nonpolyposis Colorectal Cancer (I-INPCC) is an autosomal dominant syndrome characterized by predisposition to develop a number of neoplasms including colorectal, endometrium, urinary, extracolonic gastrointestinal, brain and ovarian cancers. HNPCC is caused by inherited mutations in DNA Mismatch Repair (MMR) genes. Defective DNA Mismatch Repair results in genetic instability, which can easily be owerved inshort repetitive sequences as microsatellites (Microsatellite Instability, MSI). An international workshop on MSIheld in Bethesda in 1997 proposed a panel of live microsatellite markers to be used in MSI analysis. This panelincludes two mononucleotide repeats (BAT25, BAT26) and three dinucleotide repeats (D2SI23, D5S346 andDI7S250). In our laboratory we are currently using a di&`erent microsatellite panel composed by threemononucleotide repeats (BAT25, BAT26, BAT40) and two dimmleotide repeats (D2SI23 and Dl8S57). 'I`heaim of this study was to evaluate the specificity ofthe Bethesda markers, as compared with our panel, to idmtifyMLHI and MSIE mutation—positive IINPCC. We compared the results of MSI-analysis in cancer from 27HNPCC Iizmilies (according to the Amsterdam criteria II) and ii•om 75 families in which not all the Amsterdamcriteria were met (Suspected IINPCC), using both the Bethesda and the alternative panel. In addition,immunohistochemistry of MLIII and MSH2 proteins was pertbrmed in all tumors in order to study thecorrelation between the two MSI-panels and the expression of MLIII and MSIE proteins.Using the Bethesda markers, 49 (48%) of tumors showed MSI. On the other hand, using the alternative panel, 33(32,3%) of tumors and displayed MSI. Loss of MLHI or MSIE was evident in 25 of 49 (5I%) MSI tumorsaccording to the Bethesda panel, whereas with the alternative panel 25 of 33 (75,7%) MSI tumors showed noprotein expression. In this group, eleven patients were tested for germline mutations of MMR genes, and all ofthem showed constitutional alterations.Our data suggest that the Bethesda panel is more sensitive to define MSI tumors, but the proposed marker panelis more specific than the Bethesda one to identity MSI tumors with no expression of MLHI and MSIE proteins.'I`he proposed marker panel seems to have a higher predictive value in the identification o