HNPCC Testing

Spectrum Pathology announces the availability of testing for defective DNA mismatch repair in tumor tissue of patients with colorectal cancer. The testing algorithm will help to identify patients with a heritable defect in DNA mismatch repair (HNPCC syndrome).

All colorectal carcinomas will be routinely tested using a series of four immunohistochemical stains to assess the expression of DNA mismatch repair enzymes MLH1, MSH2, MSH6 and PMS2. Interpretative reports with recommendations will be issued, and abnormal test results will be discussed with you over the phone. All cases showing equivocal immunohistochemical test results and cases with discrepant clinical findings will be reflexively tested for DNA microsatellite instability and/or gene promoter hypermethylation and BRAF gene defects.

Routine testing of colorectal polyps (adenomas) is discouraged, unless there is strong clinical suspicion for HNPCC. When there is immunohistochemical loss of one or more DNA mismatch repair enzymes, it does confer the same risk probabilities and recommendations for follow-up as if in a carcinoma. However, a normal staining pattern in an adenoma does not rule out the possibility of HNPCC.

Our test results will help to stratify patients into three groups: (1) Patients with intact DNA mismatch repair and a very low likelihood of a heritable condition; (2) Patients with features of defective DNA mismatch repair which could be heritable or epigenetic; and (3) Patients with features of defective DNA mismatch repair indicative of a heritable, or less likely epigenetic cause. Consideration of further genetic counseling and/or testing will depend on the specific test result, patient history, clinical findings and family history.

 Current cases of colorectal cancer at our currently associated health care facilities (Maine Medical Center, Mercy Hospital, SMMC, Miles Memorial Hospital, Memorial Hospital, St. Andrews Hospital) are routinely tested. To facilitate accurate testing and appropriate follow-up of older (archival) cases, regardless of location, a paraffin-embedded tumor tissue block and the matching pathology report can be sent to the attention of Dr. Robert Christman or Dr. Hagen Blaszyk by the primary pathologist of that institution.