Test Overview
Test Methodology

Multiplex Polymerase Chain Reaction (PCR) with Capillary Electrophoresis

Test Usage

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.

Reference Range *

Interpretive report provided.

Test Limitations

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.

Test Details
Days Set Up
Monday - Friday
Analytic Time

5 - 10 days

Soft Order Code
MSI
MiChart Code
Microsatellite Instability Analysis
Synonyms
  • Lynch Syndrome
  • Hereditary Nonpolyposis Colorectal Cancer (HNPCC)
  • MSI
  • Microsatellite Instability
  • MLABEL
  • HNPCC Screen
  • MLH1B - MLH-1 Immunostain
  • MSH2B - MSH-2 Immunostain
  • MSH6B - MSH-6 Immunostain
  • PMS2B - PMS-2 Immunostain
  • SLIDEM - Slide Review, Mol Genetics
Laboratory
Molecular Diagnostics
Section
Molecular Diagnostics
Specimen Requirements
Collection Instructions

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.

Alternate Specimen
This test may also be performed on a non-invasive adenoma; however, it should be noted that MSI testing is much more sensitive for Lynch Syndrome when performed on an invasive tumor. Up to 50% of adenomas in patients with Lynch Syndrome may not demonstrate microsatellite instability. The intention to evaluate a non-invasive adenoma should be clearly indicated on the requisition and a report specific for adenomas will be issued.
Normal Volume
Formalin-fixed, paraffin-embedded tissue. Extracted DNA is also acceptable if extracted in a CLIA certified laboratory.
Additional Information

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.

Billing
CPT Code
81301, 88381-TC
Fee Code
21676, NA037
Pro Fee CPT
G0452-26, 88381-26
NY State Approved
No