Inherited Cancer Syndromes • Molecular Genetics Microsatellite Instability (MSI) with Immunohistochemistry (IHC)

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Test Code:

4850
Department:

Inherited Cancer Syndromes • Molecular Genetics
Test Synonyms:

Hereditary Nonpolyposis Colorectal Cancer Mismatch repair genes and proteins • Colorectal cancer • MLH1 • MSH2 • MSH6 • PMS2 • HNPCC
CPT Code(s):

81301 • 88387 • G0452 • 88342

Background:

Microsatellites are short, tandemly repeated DNA sequences from 1-6 base pairs in length. Microsatellite markers can be used to detect a form of genetic instability called Microsatellite Instability (MSI)^1,2. MSI is a consequence of germline or somatic inactivation of mismatch repair genes (including MSH2, MSH6, MLH1 and PMS2). Loss or downregulation of the expression of the protein products of these genes results in failure of the DNA mismatch repair system. Due to their repetitive sequence composition, microsatellite sequences are especially vulnerable to faulty DA mismatch repair genes, resulting in expansion or contraction of the microsatellite segment. Such changes are detectable by comparing microsatellite allele size variations between matching normal and tumor samples.

Further, loss of mismatch repair proteins can be detected by immunohistochemical staining (IHC) of tumor tissue. At OHSU, we have IHC assays for MLH1, MSH2, MSH6, and PMS2. IHC is performed in parallel with MSI PCR testing and consolidated into one report.

*All samples which are MSI high and MLH1 unstained by IHC can be reflexed to BRAF testing to aid in the determination of the genetic basis of the individual’s colorectal cancer, i.e., hereditary vs. sporadic, for additional charge. (Please contact Client Services at (855) 535-1522 to add BRAF testing.)

Reasons for Referral:

Lynch Syndrome MSI plus IHC is a tumor screening test for all newly diagnosed colorectal cancer patients to identify patients who may have an inherited form of colorectal cancer (Hereditary Nonpolyposis Colon Cancer or Lynch Syndrome). About 15% of patients having MSI tumors have Lynch Syndrome, while the remaining have a sporadic form of CRC; 95% of patients with Lynch Syndrome have MSI. Patients with MSI tumors and the absence of a specific mismatch repair gene can be tested by mutation analysis to identify the gene defect. Family members at risk for having inherited the familial mutation can be tested to determine whether they are at risk for developing CRC due to Lynch Syndrome and if so, undergo frequent surveillance screening.

Methodology:

PCR: Fluorescently labeled primers for coamplification of five mononucleotide repeat markers (BAT-25, BAT-26, NR-21, NR-24 and MONO-27).

IHC: Standard immunohistochemical staining on sections of formal-fixed paraffin-embedded tissue, using a biotin-free detection system with primary antibodies MLH1-G168-728, MSH2-G219-1129, MSH6-clone 44, PMS2-A-16-2.

Samples with instability in two or more of these mononucleotide markers are designated MSI-High (MSI-H), whereas those with one unstable marker are designated MSI-Low (MSI-L). Samples with no detectable alterations are MSI-stable (MSS). These designations are in accordance with the National Cancer Institute’s Bethesda guidelines.

Specimen Requirements:

Preferred:

-1 paraffin tissue block of tumor with minimal normal tissue

If tissue blocks cannot be sent:

Tumor: 5 unstained slides of Tumor at 5 micron + 1 H&E

DNA: 200ng at 50-100ng/µL (DNA must be extracted in a CLIA-certified laboratory or a laboratory meeting equivalent requirements as determined by the CAP and/or CMS)

A REQUISITION FORM MUST ACCOMPANY ALL SAMPLES. Please include detailed clinical information, including ethnicity, clinical history, and family history.

Test Performed (Days):

Weekly

Turn Around Time:

7 - 14 days

Shipment Sensitivity Requirements: