Colon & Colorectal Cancer · Article 167

When Should Lynch Syndrome Be Suspected and Tested For?

Lynch syndrome testing requires a structured, evidence-based clinical approach. This review summarizes the key diagnostic, management, monitoring and decision points for gastroenterology and hepatology practice.

Lynch syndrome testing clinical reference — Related free clinical resource: Images in Gastroenterology and Hepatology.

Lynch syndrome testing: practical clinical approach

This page focuses on Lynch syndrome testing with emphasis on decisions that change patient care, common pitfalls, and the current evidence base.

External guidance for Lynch syndrome testing

Clinical takeaway: For Lynch syndrome testing, decisions should integrate current guidelines, patient-specific risk, and the evidence summarized below.

Answer first: Lynch syndrome should be considered in patients with colorectal or endometrial cancer at a young age, multiple Lynch-associated cancers, a suggestive family history, or abnormal tumor mismatch-repair testing. Universal mismatch-repair immunohistochemistry or microsatellite-instability testing of newly diagnosed colorectal cancers is now standard in many systems because family-history criteria alone miss affected families. Abnormal tumor testing should trigger appropriate germline evaluation and genetic counseling.

Tumor testing has changed case finding

Loss of mismatch-repair protein expression or microsatellite instability identifies patients who need further evaluation.

Family history still matters

Ask about colorectal, endometrial, ovarian, gastric, urinary tract and other Lynch-associated cancers on both maternal and paternal sides.

Testing the right person matters

Whenever possible, germline testing begins with an affected individual because interpretation is more informative.

Practical clinical algorithm

1. Review age at cancer diagnosis and family history.

2. Confirm tumor MMR/MSI results for colorectal cancer.

3. If abnormal, distinguish sporadic pathways such as MLH1 methylation when appropriate.

4. Refer for genetic counseling and germline testing.

5. Offer cascade testing to relatives when a pathogenic variant is found.

Common mistakes to avoid

Relying only on the Amsterdam criteria.
Ignoring endometrial cancer history.
Testing an unaffected relative first when an affected relative is available.
Failing to explain implications for relatives.
Not adjusting colonoscopy intervals after diagnosis.

Trainee takeaway

Lynch syndrome is increasingly found through tumor biology rather than pedigree alone; every colorectal cancer deserves attention to mismatch-repair status.

Frequently asked questions

Does every CRC need Lynch testing?

Universal tumor MMR/MSI testing is widely recommended.

Is MSI-high always Lynch syndrome?

No. Some cases are sporadic, especially MLH1-deficient tumors with methylation.

Why does diagnosis matter?

It changes cancer surveillance, treatment implications and testing for relatives.

References

1. Thomson ABR. Practice Review in Gastroenterology. CAPstone Academic Publishers; 2014.

2. Thomson ABR. Guideline-Based Management in Gastroenterology. CAPstone Academic Publishers; 2015.

3. Syngal S, Brand RE, Church JM, et al. ACG Clinical Guideline: Genetic Testing and Management of Hereditary GI Cancer Syndromes. Am J Gastroenterol. 2015;110:223-262.

Educational content only. Clinical decisions should incorporate the individual patient, local resources, product labeling, and the most current applicable guideline or regulatory information.

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