Clinical Significance:
Recently established guidelines from the American Society for Clinical Pathology (ASCP), College of American Pathologists (CAP), Association for Molecular Pathology (AMP) and/or the American Society of Clinical Oncology (ASCP) recommend microsatellite Instability (MSI) testing for all newly diagnosed patients with colon cancer.

MSI-H tumors are reflexed to MMR IHC testing and BRAF V600 mutation, as this mutation only rarely occurs in Lynch syndrome, its presence helps to identify sporadic (non-germline) MSI-H.

https://www.nccn.org/professionals/physician_gls/pdf/colon.pdf

Specimen Requirements and Collection:
Formalin fixed tissue containing a sufficient amount of tumor (generally at least several mm of tumor tissue submitted in the tissue block).  The MSI assay utilized by our laboratory will detect mutations as long as they constitute at least 10% of the DNA sample mix.

Methodology:
DNA extraction, PCR, and capillary electrophoresis

Forms:
Molecular Pathology requisition form

Transport:
Send formalin-fixed, paraffin-embedded (FFPE) tissue and cell block containing tumor at room temperature.  Also acceptable 10-unstained, 4-5 micron slides with 1 post H&E.  Please include a surgical pathology report

Unacceptable specimen:
Specimens fixed in alternative fixatives or metal fixatives (ex. B-plus).  Decalcified specimens.

Reference Range:
Microsatellite Stable (MSS) = none of the 5 microsatellite markers unstable
High Microsatellite instability (MSI-H) = >/= 2 of 5 microsatellite markers unstable
Low Microsatellite instability (MSI-L) = 1 of 5 microsatellite markers unstable

CPT codes:
88381, 81210, 81301, G0452

Test reported:
Results are reported within 7-10 days