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Microsatellite Instability

CPT 81301; 88381
  • Colorectal Cancer Screening
  • Hereditary Nonpolyposis Colorectal Cancer, Screening
  • Mismatch Repair Defect
  • Replication Repair (RER)

Test Details

Cancer Type

Colorectal cancer (CRC), Endometrial, Hereditary cancer, Lynch syndrome

Technology Used


Turnaround Time

10 - 14 days


Identify tumors with microsatellite instability. High-frequency microsatellite instability (MSI-H) is associated with Lynch syndrome, but it is also found in 15% to 20% of sporadic colorectal and endometrial cancers. Lynch syndrome is an autosomal-dominant inherited cancer syndrome that predisposes to colorectal, endometrial, gastric, ovarian, upper urinary tract, and other cancers. MSI-High status may enhance the likelihood of tumor responsiveness to immune checkpoint inhibitor therapy.

Special Instructions

This assay needs both (1) DNA prepared from FFPE (formalin-fixed and paraffin-embedded) tumor tissue and (2) matched normal tissue (FFPE or blood). Please provide a copy of the pathology report. This test will be delayed if the pathology report is not received. Please direct any questions regarding this test to customer service at 800-345-4363.


MSI-H is a marker of underlying DNA mismatch repair defect but does not define specific gene mutations responsible for cancers. If direct testing for gene mutations responsible for Lynch syndrome is desired, please call customer service at 800-345-4363 for more information. This assay can detect 8% to 12% of mutant in a background of wild-type genomic DNA.

This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.


Multiplex polymerase chain reaction (PCR); capillary electrophoresis

Specimen Requirements

Information on collection, storage, and volume


One paraffin-embedded tumor and either whole blood or paraffin-embedded normal tissue


Eight unstained slides at 5 μM and one matching H&E slide or FFPE tissue block or 3-5 mL whole blood

Minimum Volume

Samples with ≥4 mm² tumor and normal tissue surface area and ≥50% tumor content are preferred; 3 mL whole blood


FFPE tissue block or slides, lavender-top (EDTA) tube or green-top (sodium heparin) tube, tan-top (K2-EDTA) tube or pink-top (K2-EDTA) tube

Storage Instructions

Blocks and slides at room temperature; whole blood at 2°C to 8°C

Causes for Rejection

Tumor block containing insufficient tumor tissue or no tumor; broken or stained slides. Whole blood: Contaminated specimen; frozen whole blood received; leaking tube; clotted blood; hemolysis; specimen containing suspicious foreign material; quantity not sufficient for analysis