Newly Diagnosed With Colorectal Cancer: Lynch Syndrome and Hereditary Testing
Hereditary testing is commonly discussed after a colorectal cancer diagnosis. This page explains what testing is recommended, why the type of test matters, and what results mean for your family.
What You Should Know About Hereditary Testing After a Colorectal Diagnosis
- Approximately 3-5% of colorectal cancers are caused by an inherited syndrome, most commonly Lynch syndrome.
- Many hospitals routinely test colorectal tumors for signs of Lynch syndrome using MSI (microsatellite instability) or IHC (immunohistochemistry) testing. This is tumor testing — it is not the same as germline genetic testing.
- If your tumor shows MSI-High or MMR-deficient results, germline genetic testing is typically the next step to confirm whether you carry a heritable Lynch syndrome mutation.
- A Lynch syndrome diagnosis has significant implications for your family — first-degree relatives each have a 50% chance of carrying the mutation.
What Hereditary Testing Means After a Colorectal Cancer Diagnosis
Lynch syndrome is caused by mutations in mismatch repair (MMR) genes: MSH2, MLH1, MSH6, PMS2, and EPCAM. It raises the risk of colorectal, uterine, ovarian, and several other cancers. It is the most common hereditary colorectal cancer syndrome.
Not all colorectal cancers with MSI-High tumors are caused by inherited Lynch syndrome — some are caused by acquired (somatic) mutations. Germline genetic testing distinguishes heritable Lynch syndrome from sporadic MSI-High tumors.
What Usually Happens Next
If your tumor has not yet been tested for MSI/MMR status, ask your oncologist. Universal tumor testing is recommended by NCCN for all colorectal cancer patients.
If MSI-High or MMR-deficient results were found, or if your family history suggests hereditary risk, a genetic counselor will review whether germline testing is indicated and arrange it.
Tumor Screening vs Germline Lynch Syndrome Testing — What the Difference Means for You
Tumor (somatic) testing: MSI and IHC
MSI and IHC testing analyze the tumor itself for features associated with Lynch syndrome. These are often done automatically at diagnosis. An MSI-High or MMR-deficient result is a signal — not a diagnosis — that hereditary Lynch syndrome may be present.
Germline testing: the definitive test
Germline genetic testing analyzes your DNA directly to identify whether you carry a heritable MMR gene mutation. This is the definitive test for Lynch syndrome. It is the test that tells you — and your family — whether a mutation is inherited.
Why both tests matter
Tumor testing guides treatment decisions (including immunotherapy eligibility). Germline testing guides long-term surveillance, prevention, and family risk assessment. They serve different purposes and both may be relevant to your situation.
If your tumor was MSI-High but germline testing was negative
This occurs when the tumor’s MSI-High status is caused by an acquired (somatic) mutation rather than an inherited one. It does not indicate hereditary Lynch syndrome, but your oncologist may still consider it relevant to treatment decisions.
What a Lynch Syndrome Diagnosis Means for Your Family
If germline Lynch syndrome is confirmed, each of your first-degree relatives has a 50% chance of carrying the same mutation. Lynch syndrome raises risk for colorectal, uterine, ovarian, stomach, and several other cancers.
Relatives who carry a Lynch syndrome mutation benefit from significantly more frequent colonoscopy — typically every one to two years starting in their 20s or 30s, compared to every ten years for the general population.
- First-degree relatives (parents, siblings, children) — 50% chance if mutation confirmed
- Female relatives face additional uterine and ovarian cancer risk depending on which Lynch gene is mutated
- The specific surveillance recommendations depend on which MMR gene is affected
How LifeShield Can Help
Lynch syndrome germline panel
Covers MSH2, MLH1, MSH6, PMS2, EPCAM, and all clinically significant Lynch-associated genes
Genetic counseling
Review of your tumor testing results, family history, and clinical context before and after germline testing
Results coordination
Results summary to share with your oncology team and gastroenterologist
Family cascade support
Guidance for relatives who want to understand their own Lynch syndrome risk
Reviewed by LifeShield Medical Team · Last reviewed March 2026
Frequently Asked Questions
MSI (microsatellite instability) testing is performed on the tumor. It looks for features associated with Lynch syndrome but does not confirm a heritable mutation. Lynch syndrome genetic testing is performed on your DNA. It identifies whether you carry an inherited MMR gene mutation — which is the definitive test for Lynch syndrome.
Not necessarily. MSI-High tumors are associated with Lynch syndrome, but some MSI-High colorectal cancers are caused by acquired (somatic) mutations rather than inherited ones. Germline genetic testing is needed to distinguish the two.
NCCN recommends tumor MSI/IHC testing for all colorectal cancer patients. Germline genetic testing is recommended based on tumor results, family history, and age at diagnosis. A genetic counselor will review whether germline testing is indicated for your situation.
People with Lynch syndrome typically require colonoscopy every one to two years starting in their 20s or 30s — significantly more frequently than the general population. Female Lynch syndrome carriers also benefit from uterine and ovarian cancer surveillance. The specific recommendations depend on which gene is mutated.
Most eligible patients qualify for coverage when NCCN criteria are met. A colorectal cancer diagnosis with MSI-High or MMR-deficient tumor results typically meets those criteria. LifeShield provides insurance support and superbill assistance for all patients.
Ready to Take the Next Step?
When you are ready, a licensed genetic counselor can help you understand your options and build a clear plan.
Medical Disclaimer: This content is for informational purposes only and does not constitute medical advice. It is based on published NCCN clinical guidelines and peer-reviewed research. Always consult a qualified healthcare provider for medical decisions. LifeShield content is reviewed by board-certified genetic counselors.