Test Details
Methodology
Immunohistochemistry
Use
Microsatellite instability (MSI) and/or immunohistochemistry (IHC) testing is performed to analyze colon and other tumor tissue samples to determine if the tumor is microsatellite unstable. MSI testing can detect an abnormal number of microsatellite repeats, which indicates a defective mismatch repair (MMR) gene and microsatellite instability. A missing protein detected by IHC suggests a mutation in the gene.
Many solid tumors can be microsatellite instability-high (MSI-H or dMMR), including colorectal, endometrial, biliary,
gastric, pancreatic, breast and prostate cancer. IHC testing for MMR protein loss can help identify patients with dMMR or MSI-H tumors that may benefit from immune checkpoint inhibitor therapy (e.g., Nivolumab, Pembrolizumab).
This test may also be used to screen for Lynch Syndrome. Depending on the IHC results, additional molecular or genetic testing may be indicated.
Limitations
Uses of fixatives other than 10% neutral-buffered formalin and decalcified specimens may not yield reliable results.
Specimen Requirements
Specimen
Formalin-fixed, paraffin-embedded (FFPE) tumor (colorectal cancer (CRC); endometrial, gastric, hereditary cancer; Lynch Syndrome)
Volume
One paraffin block or eight unstained, positively-charged tissue slides cut at 4-5 microns
Minimum Volume
Eight unstained slides
Container
Paraffin block transport pouch or slide mailer
Collection Instructions
Formalin fixed, paraffin-embedded tissue block or slides
Stability Requirements
| Temperature | Period |
|---|---|
| Room temperature | 30 days (stability provided by manufacturer or literature reference) |
Storage Instructions
Maintain specimen at room temperature.
Causes for Rejection
No tumor tissue in FFPE blocks or slides; broken or stained slides