Molecular Genetic Testing
Colon Cancer, Hereditary Non Polyposis (HNPCC): Microsatellite Instability (MSI) for Cancer Detection and Familial Predisposit

Indication and Diagnostic Value

10% of all colorectal carcinomas have a hereditary background. The most common form is HNPCC characterized by early age of onset, very small number of colorectal polyps and presence of different extra-colonic malignancies (endometrial, stomach, urinary tract and others).
MSI is caused by a failure of the DNA mismatch repair system to repair errors that occur during the replication of DNA and is characterized by the accelerated accumulation of single nucleotide mutations and alterations in the length of repetitive microsatellite sequences. The presence of MSI in tumor tissue is associated with certain unique clinical and pathological characteristics. It is a striking feature of HNPCC that MSI is seen in most HNPCC tumours and in a proportion of nonhereditary colorectal tumours. Therefore, testing for MSI in HNPCC patients is strongly recommended as a pre-screening test because it identifies patients, which are to be subjected to the more expansive MLH1 and MSH2 mutation screening.

Samples and Test Method

Fresh or fixed tumor specimens are required. Microdisssection of pathological specimens is recommended to enrich for neoplastic tissue; and normal tissue is required to document the presence of MSI.
The test defines MSI by producing PCR fragments according to the microsatellite markers BAT25, BAT26, D10S197, D13S175 and D18S69. Fragment analysis is run on an ABI-Sequencer.

Turnaround time for this test is 10 days.

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