Multiplex Polymerase Chain Reaction (PCR) with Capillary Electrophoresis
Microsatellite instability (MSI) is the change in length of a microsatellite allele due to either insertion or deletion of repeating units and a failure of the DNA mismatch repair (MMR) system to repair these replication errors. This genomic instability arises in a variety of human neoplasms where tumor cells have a decreased ability to faithfully replicate DNA. MSI is particularly associated with colorectal cancer, where 15-20% of sporadic tumors show MSI, in contrast to the more common chromosomal instability (CIN) phenotype, with MSI status being an independent prognostic indicator. MSI analysis is also clinically useful in identifying patients at increased risk of hereditary nonpolyposis colorectal cancer (HNPCC)/Lynch Syndrome, where a germline mutation of a MMR gene causes a familial predisposition to colorectal cancer.
Interpretive report provided.
The detection of microsatellite instability in neoplastic tissue may suggest a predisposition to cancer associated with hereditary nonpolyposis colorectal cancer (HNPCC; Lynch Syndrome). However, microsatellite instability may also occur as a sporadic phenomenon, particularly in cancers with somatic methylation of the MLH1 promoter. Microsatellite testing may rarely be stable in neoplasms associated with HNPCC, particularly in individuals with with germline mutations of MSH6. In addition, the absence of microsatellite instability does not exclude the possibility that the patient's neoplasm is due to an inherited defect in a gene not involved in mismatch repair. Clinicopathologic correlation, genetic counseling and additional testing may be indicated including immunohistochemistry, BRAF V600E testing, MLH1 promoter methylation testing and/or mismatch repair gene sequencing/deletion analysis.
5 - 10 days
- Lynch Syndrome
- Hereditary Nonpolyposis Colorectal Cancer (HNPCC)
- Microsatellite Instability
- HNPCC Screen
- MLH1B - MLH-1 Immunostain
- MSH2B - MSH-2 Immunostain
- MSH6B - MSH-6 Immunostain
- PMS2B - PMS-2 Immunostain
- SLIDEM - Slide Review, Mol Genetics
Both normal (non-neoplastic) and invasive neoplastic tissue are required for analysis. A formalin-fixed, paraffin-embedded tissue block is preferred but unstained, UNBAKED slides (5-8, 10-micron slides; 10-15 if few neoplastic cells are present) with associated H&E stained slide are also acceptable. The appropriate block/slides should contain an area with a high percentage of invasive neoplastic cells (for micro-/macro-dissection). Either the same block/slides or separate block/slides must contain an area of pure, non-neoplastic tissue of sufficient cellularity. Decalcified tissue or other fixatives will be accepted and the assay attempted, however these may result in failed testing due to degraded nucleic acid. Both blocks and slides should be stored at room temperature.
By ordering this test the clinician acknowledges that informed consent has been obtained from the patient as required by applicable state or federal laws and the ordering clinician has authorization from the patient permitting MLabs to report the test results to the ordering clinician. Test includes microdissection billed as a separate additional charge. Test includes pathologist interpretation of results billed as a separate additional charge. This test is not available without interpretation.