Test Overview
Test Methodology

Methylation-specific real-time PCR

Test Usage

Hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch Syndrome, is an autosomal dominant condition associated with increased risk of multiple cancers particularly colorectal and endometrial. This syndrome most commonly results from mutations of genes encoding DNA mismatch repair proteins including MLH1, MSH2, MSH6 and PMS2. These mutations lead to tumors with microsatellite instability (MSI) – a change in length of a microsatellite allele due to either insertion or deletion of repeating units. However, MSI can also be seen in sporadic colorectal and endometrial cancers that are not associated with HNPCC. The majority of cancers with sporadic MSI demonstrate hypermethylation of the MLH1 promoter resulting in silenced MLH1 protein expression. MLH1 promoter hypermethylation is extremely uncommon in tumors from patients with HNPCC. Similarly, BRAF V600E mutations are frequently observed in colorectal carcinoma with sporadic MSI and are virtually never observed in tumors associated with HNPCC. Therefore, the evaluation of neoplastic cells for MLH1 promoter methylation and/or BRAF V600E can be useful in screening colorectal cancers with MSI for suspected HNPCC. MLH1 promoter methylation is particularly useful in evaluating endometrial carcinomas with MSI since BRAF V600E mutations are extremely rare in these tumors.

In this assay, MLH1 promoter methylation is detected using methylation specific real-time PCR (MethyLight). The absence of MLH1 promoter methylation in tumors demonstrating loss of MLH1 protein expression and/or MSI may suggest a MLH1 mutation associated with HNPCC. Genetic testing for germline MLH1 mutation is recommended in this setting. Conversely, the presence of MLH1 promoter methylation in neoplastic tissue is suggestive of sporadic MSI, not associated with HNPCC. However, rare instances of co-occurring MLH1 promoter hypermethylation and MLH1 germline mutations have been described. In addition, constitutional epimutations that result in heritable MLH1 promoter hypermethylation also exist, conferring an HNPCC (Lynch Syndrome) phenotype even in the absence of primary sequence alternations in the MLH1 gene. If there is a clinical suspicion of germline MLH1 promoter methylation, performing germline MLH1 promoter methylation testing on peripheral blood is recommended. Genetic counseling may be indicated based on the clinical and laboratory findings.

Reference Range *

Interpretive report provided.

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Test Limitations

Specimens submitted for Molecular Diagnostics testing may contain substances that can inhibit PCR gene amplification. If an inhibitor is known to be present, attempts will be made to clear the specimen of inhibitor prior to amplification. Known inhibitors include heparin, medications and some levels of hemoglobin or IgG.

Test Details
Days Set Up
Monday through Friday
Analytic Time

3 - 10 days

Soft Order Code
MLH1M
MiChart Code
MLH1 Promotor Methylation
Synonyms
  • Hereditary Nonpolyposis Colorectal Cancer (HNPCC)
  • Lynch Syndrome
Laboratory
Molecular Diagnostics
Section
Molecular Diagnostics
Specimen Requirements
Collection Instructions

Send formalin-fixed paraffin-embedded block containing tumor tissue stored at room temperature. If sending slides, please send 1 H&E slide containing tumor tissue, and 8 unbaked, 10 micron thick unstained slides of the same tissue. Please include any pertinent history.

Alternate Specimen
Slides will be accepted: send 8 unbaked, unstained slides (10 micron) and 1 H&E stained slide.
Rejection Criteria
B5 or Picric acid fixed paraffin embedded tissue is not acceptable
Normal Volume
Formalin-fixed, paraffin-embedded tissue. Extracted DNA is also acceptable if extracted in a CLIA certified laboratory.
Additional Information

By ordering this test the clinician acknowledges that informed consent has been obtained from the patient as required by applicable state or federal laws and the ordering clinician has authorization from the patient permitting MLabs to report the test results to the ordering clinician. Test includes microdissection billed as a separate additional charge. Test includes pathologist interpretation of results billed as a separate additional charge. This test is not available without interpretation.

Billing
CPT Code
81288, 88381-TC
Fee Code
NA071, NA037
Pro Fee CPT
G0452-26, 88381-26
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