Microsatellite Instability (MSI) by PCR
Also known as: Microsatellite Instability Analysis
Use
This assay uses PCR and fragment analysis on paired normal and tumor tissue to determine microsatellite instability (MSI) across the standard five NCI-recommended loci. A result interpreted as MSI-high indicates at least two unstable markers, while MSI-low indicates only one unstable marker. This testing supports the assessment of mismatch repair deficiency and MSI status, which can have implications for Lynch syndrome screening and therapeutic decision-making in oncology.
Special Instructions
Testing requires submission of both a normal (non‑tumor) tissue sample or blood and a tumor sample. At least 20% tumor content in tumor samples (post-macrodissection) is required. Submit specimens using one requisition form; label normal samples as “normal tissue.” Transport blocks with cold pack not directly in contact; slides may be shipped at room temperature.
Limitations
Tumor samples must meet minimal tumor content (≥20%); inadequate or improperly labeled normal tissue may compromise analysis. Slides must be prepared using 10% neutral buffered formalin and positively charged slides; zinc fixatives are not acceptable. Fragment analysis is limited to the five standard loci, and interpretation is categorical (MSI‑high, MSI‑low) without quantitative mutation burden.
New York Approved
Methodology
PCR-based (PCR)
Biomarkers
Result Turnaround Time
7 days
Related Documents
For more information, please review the documents below
Specimen
Whole Blood
Volume
5 mL peripheral blood in EDTA tube
Minimum Volume
Not provided
Container
EDTA tube
Collection Instructions
Label as normal tissue