Ordering Guidance

This test is not recommended as a first-tier screening measure for hereditary nonpolyposis colon cancer. For more information see TMSI / Microsatellite Instability, Tumor and IHC / Mismatch Repair (MMR) Protein Immunohistochemistry Only, Tumor.

Testing will only be performed on colon or endometrial tumors demonstrating loss of MLH1 protein expression by immunohistochemistry.

Mayo Clinic's preferred screening test includes both MLH1 promoter hypermethylation and BRAF V600E testing. Order BRMLH / MLH1 Hypermethylation and BRAF Mutation Analysis, Tumor.

Extracted DNA from tissues is not an acceptable specimen type.

If the MMR immunohistochemistry (IHC) results for MLH1 and/or PMS2 suggest possible tumor heterogeneity, are ambiguous, or unusual, the physical IHC stains will be required to optimize the area of tissue selected for testing and for interpretation of the results. If IHC stains are required and not sent with the specimen, a request will be submitted to provide the IHC stains which will result in a slight delay.

Necessary Information

Pathology report and MMR IHC results must accompany specimen in order for testing to be performed.

Specimen Required

Specimen Type: Tissue block or slide

Collection Instructions:

1. Submit formalin-fixed, paraffin-embedded tissue block (preferred) or 1 slide stained with hematoxylin and eosin and 10 unstained, nonbaked slides (5-micron thick sections) of the tumor tissue.

2. Sections should contain tumor tissue.