What should you know about mismatch repair immunohistochemistry?

Cells constantly correct copying errors in their DNA. Mismatch repair proteins help with that correction. Immunohistochemistry uses laboratory stains to show whether selected repair proteins are present in a tumour sample.

A result may show retained expression of the tested proteins or loss of one or more proteins. Loss can suggest mismatch repair deficiency, but it does not by itself prove an inherited condition. The result must be interpreted with the tumour type, family history, and other pathology findings.

Ask which proteins were tested, whether the sample was adequate, and whether the finding is clear or needs another test. Your clinician may recommend genetic counselling or germline testing when the pattern and personal or family history raise concern for an inherited syndrome.

The result can also influence discussion of treatment options in some cancers. Keep a copy of the pathology report and ask whether relatives need advice. A biopsy is the usual source of the tissue used for this laboratory assessment.

This is a laboratory result rather than a procedure that causes new symptoms. Contact your care team if the report is difficult to understand, if a genetic referral was advised, or if you are worried about what it means for relatives. Seek urgent care for symptoms from your cancer or treatment, such as severe pain, breathing difficulty, or sudden confusion.

Ask whether the result is proficient or deficient, what the staining pattern means, whether another test is needed, and whether genetic counselling is appropriate. Ask how the finding affects treatment choices and what it means for close relatives.