Mismatch Repair by Immunohistochemistry, with Interpretation
Also known as: MSI
Use
This test is a first-line screening tool for Lynch syndrome, also known as Hereditary Nonpolyposis Colorectal Cancer (HNPCC). Immunohistochemical staining for mismatch repair proteins can be used as a surrogate test for assessing microsatellite instability, a hallmark of Lynch syndrome. Abnormal results suggest microsatellite instability, which qualifies patients for immune checkpoint inhibitor treatment and can guide subsequent germline evaluation of mismatch repair genes. Genetic counseling is recommended for interpreting test results.
Special Instructions
The test requires tissue clearly identified as carcinoma. Provide the surgical pathology report along with the sample. Use an electronic request or an ARUP requisition form with complete client number. Multiple specimens need specific instructions for pathologist selection of the best block or individual orders. A Pathologist Block Selection Fee may apply if the pathologist is to choose the suitable specimen.
Limitations
This test is not cleared or approved by the FDA, despite being developed by ARUP Laboratories. The performance characteristics of this laboratory-developed test (LDT) were determined by ARUP Laboratories. It is intended for clinical purposes but has limitations in detection due to potential suboptimal fixation or insufficient tissue or tumor presence in the sample. Ideal for formalin-fixed, paraffin-embedded tissues without decalcified samples.
New York Approved
Methodology
Immunoassay (IHC)
Biomarkers
LOINC Codes
- 94736-6
- 50595-8
- 50322-7
- 50323-5
- 50324-3
- 50328-4
- 31208-2
Result Turnaround Time
1-5 days
Related Documents
For more information, please review the documents below
Specimen
Tissue (FFPE)
Volume
Not provided
Minimum Volume
Not provided
Container
Tissue block or 10 unstained, 3-5 micron thick, positively charged slides
Collection Instructions
Formalin fix (10 percent neutral buffered formalin is preferred) and paraffin embed specimen. If sending precut slides, do not oven bake. Transport in a tissue transport kit (ARUP supply #47808).
Storage Instructions
Protect paraffin block and/or slides from excessive heat. Ship in cooled container during summer months.
Causes for Rejection
Paraffin block with no tumor tissue remaining or specimens fixed in any fixative other than 10 percent neutral buffered formalin. Decalcified specimens.
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | Indefinitely |
| Refrigerated | Indefinitely |
| Frozen | Unacceptable |