MSI by IHC

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General Information

Lab Name
Lab Code
669
Description
For MSI PCR testing see separate test (Microsatellite Instability DNA test, mnemonic "MSI"). MSI testing by immunohistochemistry measures the presence or absence of immunoreactivity for MLH1, PMS2, MSH2 and MSH6 mismatch repair gene products in tumor tissue. One advantage of this form of testing over PCR-based microsatellite instability testing is that the results suggest which gene products are involved. DNA sequencing of the affected gene(s), such as with the ColoSeq™ Lynch and Polyposis panel is needed confirm an underlying genetic abnormality. MLH1/PMS2 and MSH2/MSH6 are typically expressed together as functional units meaning that MLH1/PMS2 and MSH2/MSH6 immunoreactivity is often lost together when absent. Isolated loss of either PMS2 or MSH6 is typically due to a mutational event and is correlated with Lynch syndrome (HNPCC). Loss of MLH1 expression is most commonly due to promoter methylation. Patients with Lynch syndrome frequently are positive for BRAF mutations and negative for MLH1 promoter hypermethylation in tumor tissue. Additional testing for MSI by PCR, BRAF mutations and/or MLH1 promoter hypermethylation may have utility in some cases. This testing is performed in Pathology's Immunohistochemistry Laboratory. Please call (206) 598-4202 for information. Or check the Pathology website found at: Pathology's Immunohistochemistry
Synonyms
colon cancer, hMLH1, hMSH2, hMSH6, HNPCC, ICC, IHC, immunohistochemistry, ip msi, Lynch syndrome, microsatellite instability, MLH1, MSH2, MSH6, MSI, Muir-Torre, PMS2
Components

Interpretation

Guidelines
Method
Immunohistochemistry
Reference Range
Ref. Range Notes
No loss of expression

Ordering & Collection

Specimen Type
Cancer tissue
Collection
Send EITHER (a) slides, OR (b) tissue block:  

(a) Instructions for slide specimens: 1 slide at 4-micron thickness stained with hematoxylin-and-eosin AND 10 unstained, baked, charged slides at 4-micron thickness Note: Sections should contain as much tumor tissue as possible.  

(b) Instructions for tissue block specimen: Provide complete tissue block containing tumor tissue. If there is more than one tissue block, please provide the block that has the greatest amount of tumor tissue. Biopsy acceptable if non-necrotic tumor fragment is 0.3 cm in maximum dimension and normal mucosa is also present. Tissue block will be returned at completion of testing.
Quantity
Requested: Slides OR Tissue block as noted above
Minimum: A minimum of 10 unstained slides

Processing

Receiving Instructions
SPS, do not log in. Place sample and requisition in Genetics Lab bucket at UW-MT and notify Genetics at 598-6429.
Misc Sendout

Performance

Lab Department
Frequency
Results within 48-72 hours
Available STAT?
Yes- Run within 24 hours upon receipt of specimen
Performing Location(s)
Other Locations/Notes
UW Pathology's Immunohistochemistry 1959 NE Pacific St, Seattle, WA Contact for technical assistance: 206-598-4202

Billing & Coding