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Test Code: TMSI
Description: Microsatellite instability (MSI) is detected in 90% of colon cancers that are part of the Hereditary Non-Polyposis Colorectal Carcinoma  (HNPCC) syndrome, and in 15% of sporadic colorectal carcinomas. It is the consequence of germline mutation(s) in or somatic inactivation of mismatch repair genes, such as MLH1, MSH2, MSH6, or PMS2. Due to their repetitive sequence composition, microsatellite sequences are especially vulnerable. This assay is based on multiplex PCR amplification of 5 microsatellites: BAT-25, BAT-26, MONO-27, NR-21, and NR-24. If there is a difference in the length of a certain microsatellite in the patient’s normal and tumor samples, the microsatellite is considered unstable. If two microsatellite loci (of 5) are unstable, the tumor is designated microsatellite instability high (MSI-H). If only one locus is unstable, the tumor is considered microsatellite instability low (MSI-L), and if no loci are unstable, the tumor is designated microsatellite stable (MSS).


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