Development of a Fluorescent Multiplex Assay for Detection of MSI‐High Tumors

Abstract

Determining whether a tumor exhibits microsatellite instability (MSI) is useful in identifying patients with hereditary non‐polyposis colorectal cancer and sporadic gastrointestinal cancers with defective DNA mismatch repair (MMR). The assessment of MSI status aids in establishing a clinical prognosis and may be predictive of tumor response to chemotherapy. A reference panel of five markers was suggested for MSI analysis by a National Cancer Institute (NCI) workshop in 1997 that has helped to standardize testing. But this panel of markers has limitations resulting from the inclusion of dinucleotide markers, which are less sensitive and specific for detection of tumors with MMR deficiencies compared to other types of markers that are currently available. This study demonstrates that mononucleotides are the most sensitive and specific markers for detection of tumors with defects in MMR and identifies an optimal panel of markers for detection of MSI‐H tumors. A set of 266 mono‐, di‐, tetra‐ and penta‐nucleotide repeat microsatellite markers were used to screen for MSI in colorectal tumors. The best markers for detection of MSI‐H tumors were selected for a MSI Multiplex System , which included five mononucleotide markers: BAT-25, BAT-26, NR-21, NR-24 and MONO-27 . In addition, two pentanucleotide markers were added to identify sample mix‐ups and/or contamination. We classified 153 colorectal tumors using the new MSI Multiplex System and compared the results to those obtained with a panel of 10 microsatellite markers combined with immunohistochemical (IHC) analysis. We observed 99% concordance between the two methods with nearly 100% accuracy in detection of MSI‐H tumors. Approximately 5% of the MSI‐H tumors had normal levels of four MMR proteins and as a result would have been misclassified based solely on IHC analysis, emphasizing the importance of performing MSI testing. The new MSI Multiplex System offers several distinct advantages over other methods of MSI testing in that it is both extremely sensitive and specific and amenable to high‐throughput analysis. The MSI Multiplex System meets the new recommendations proposed at the recent 2002 NCI workshop on HNPCC and MSI testing and overcomes problems inherent to the original five‐marker panel. The use of a single multiplex fluorescent MSI assay reduces the time and costs involved in MSI testing with increased reliability and accuracy and thus should facilitate widespread screening for microsatellite instability in tumors of patients with gastrointestinal cancers.

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• Microsatellite instability: a review of what the oncologist should know · 2020
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• Immunotherapy, Inflammation and Colorectal Cancer · 2020
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• Microsatellite instability status determined by next‐generation sequencing and compared with PD ‐L1 and tumor mutational burden in 11,348 patients · 2018
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• Colorectal Carcinoma: A General Overview and Future Perspectives in Colorectal Cancer · 2017
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• A molecular portrait of microsatellite instability across multiple cancers · 2017
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• Improved Detection of Microsatellite Instability in Early Colorectal Lesions. · 2015
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