||Paraffin-embedded, formalin-fixed block of tumor tissue from colon and normal tissue
- The best material of tumor tissue is pre-treatment biopsy.
- The best material of normal tissue is surgical resection or 2-4 ml of blood (with anticoagulant EDTA).
- Storage and transport temperature for paraffin-embedded, formalin-fixed tissue blocks is 20-25°C.
- Testing results cannot be guaranteed when DNA quality is poor or DNA is too fragmented due to previous tissue fixation process.
Indications for genetic testing:
- Testing of individuals with colorectal or other Lynch-associated cancers to estimate the probability of mutations in mismatch repair genes
- Determination of disease prognosis
- Genetic counseling
Microsatellite instability (MSI) is the mutational signature found in colorectal cancers that evolve as a result of inactivation of the DNA mismatch repair system. Defects in the genes involved in mismatch repair lead to an accumulation of somatic mutations in a cell, which may result in the cell becoming malignant. Germline mutations in mismatch repair genes are associated with developing hereditary non-polyposis colon cancer. Approximately 90% of colon cancers from families meeting Amsterdam criteria have MSI.