MICROSATELLITE INSTABILITY ANALYSIS - A MULTICENTER STUDY FOR RELIABILITY AND QUALITY-CONTROL

The molecular biology section of the Hereditary Non-Polyposis Colorect al Cancer study group-Germany, instituted a multicenter study to test the reliability and quality of microsatellite instability (MSI) analys is, Eight laboratories compared MSI analyses performed on 10 matched p airs of normal and tumor DNA from patients with colorectal carcinomas, A variety of techniques were applied to the detection of microsatelli te changes: (a) silver and ethidium bromide staining of polyacrylamide gels; (b) radioactive labeling; and (c) automated fluorescence detect ion, The identification of highly unstable tumors and tumors without M SI was achieved in high concordance, However, the interpretation of th e band patterns resulted in divergent classifications at several micro satellite marker loci for a large fraction of this tumor/normal panel. The data on more than 30 primers per case suggest that the enlargemen t of the microsatellite panel to more than 10 loci does not influence the results, In this study, cases with MSI in less than 10% of loci we re classified as microsatellite stable, whereas MSI was diagnosed in c ases with more than 40% of all markers unstable, We propose that a pan el of five microsatellite loci consisting of repeats with different le ngths should be analyzed in an initial analysis, When less than two ma rker loci display shifts in the microsatellite bands from tumor DNA, t he panel should be enlarged to include an additional set of five marke r loci, The number of marker loci analyzed as well as the number of un stable marker loci found should always be identified, These criteria s hould result in reports of MSI that are more comparable between studie s.