Microsatellite
Instability (MSI) Analysis
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
