Analysis of Microsatellite Instability by Melting Peak Analysis with BAT26 and BAT25 Specific Fluorescence Hybridization Probes

Abstract

Microsatellite instability (MSI) can be detected in about 15% of all colorectal cancers (CRC) as a result of defective mismatch repair. Almost all (>90%) CRC from patients with hereditary non-polyposis colorectal cancers (HNPCC) show MSI due to mutations in the hMSH2, hMLH1, and hMSH6 mismatch repair genes [1, 2, 3, 4]. MSI can also be observed in other tumors of the HNPCC tumor spectrum, e.g., gastric, ovarian, and endometrial carcinomas. In order to identify HNPCC patients, MSI analysis of the tumor DNA and immunohistochemical detection of mismatch repair expression in the tumor tissue is performed as a first step, followed by germline mutation analysis of the mismatch repair gene with loss of protein expression in the tumor tissue. In colorectal tumors, microsatellite analysis is performed by amplification of five microsatellite markers [5, 6], which are separated by gel or capillary electrophoresis and visualized using autoradiography [1], silver staining [7], or fluorescence techniques [8, 9]. A tumor with at least two unstable markers (2/5, 40%) is defined as MSI-H (high frequency microsatellite instability) [5, 6].