What is the role of mismatch repair deficiency testing in Lynch syndrome evaluation?

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What is the role of mismatch repair deficiency testing in Lynch syndrome evaluation?

Screening for Lynch syndrome begins with tumor-based assessment of mismatch repair deficiency. Immunohistochemistry on tumor tissue checks for the presence of the MMR proteins; if a protein is absent, it points to the corresponding gene being defective and helps guide germline testing. This approach uses the tumor phenotype to identify candidates for germline analysis and to distinguish likely hereditary cases from sporadic ones. While MSI testing can also be used, it isn’t the sole screen because IHC provides gene-specific information that directs targeted germline testing. Germline testing before tumor testing isn’t standard practice since many MMR deficiencies arise from somatic changes.

Screening for Lynch syndrome begins with tumor-based assessment of mismatch repair deficiency. Immunohistochemistry on tumor tissue checks for the presence of the MMR proteins; if a protein is absent, it points to the corresponding gene being defective and helps guide germline testing. This approach uses the tumor phenotype to identify candidates for germline analysis and to distinguish likely hereditary cases from sporadic ones. While MSI testing can also be used, it isn’t the sole screen because IHC provides gene-specific information that directs targeted germline testing. Germline testing before tumor testing isn’t standard practice since many MMR deficiencies arise from somatic changes.

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