Mismatch Repair by Immunohistochemistry, with Interpretation

Also known as: MSI

Clinical Use

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

Not provided.

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.

Test Details

New York Approved

Methodology

Immunoassay (IHC)

Biomarkers

4 targets

MLH1MSH2MSH6PMS2

LOINC Codes

Result Codes

94736-6 - Tissue block ID Spec
50595-8 - Path Interp Spec-Imp
50322-7 - MLH-1 Ag Tiss Ql ImStn
50323-5 - MSH-2 Ag Tiss Ql ImStn
50324-3 - MSH-6 Ag Tiss Ql ImStn
50328-4 - PMS-2 Ag Tiss Ql ImStn
31208-2 - Specimen source

Result Turnaround Time

1-5 days

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.