A Lynch syndrome genetic test looks for inherited pathogenic variants in MLH1, MSH2, MSH6, PMS2, or EPCAM that impair DNA mismatch repair and increase the risk of colorectal, endometrial, and several other cancers. The test is usually performed on blood or saliva after tumor screening, a suggestive personal or family history, or a known familial variant. A positive germline result can change colonoscopy timing, gynecologic risk management, treatment decisions, and testing for relatives. A negative result may be reassuring when a known family variant is absent, but it may remain inconclusive when no familial cause has been identified. Tumor tests such as mismatch-repair immunohistochemistry and microsatellite instability do not by themselves diagnose Lynch syndrome because some mismatch-repair-deficient tumors are sporadic. MLH1 promoter methylation, BRAF testing in colorectal cancer, paired tumor-normal sequencing, and deletion analysis can help clarify the cause. Results should be reviewed with a genetics professional because cancer risks and surveillance differ by gene.
- A pathogenic germline variant in MLH1, MSH2, MSH6, PMS2, or an EPCAM deletion confirms Lynch syndrome.
- Mismatch-repair-deficient or MSI-high tumor results suggest possible Lynch syndrome but require germline and sometimes tumor follow-up.
- Loss of MLH1 and PMS2 in a colorectal tumor is often caused by acquired MLH1 promoter methylation rather than an inherited MLH1 variant.
- A negative family-specific test usually means the person did not inherit that Lynch syndrome variant and can often return to population-based screening.
- A variant of uncertain significance does not confirm Lynch syndrome and should not direct surgery or predictive testing of relatives.
Table of Contents
- Genes and cancer risks
- Who should consider testing
- Tumor screening and germline testing
- How to interpret results
- Screening and risk reduction
- Family testing and reproductive options
- Treatment, privacy, and next steps
Genes and cancer risks
Mismatch repair is a cellular proofreading system. MLH1, MSH2, MSH6, and PMS2 proteins recognize and repair small errors that occur when DNA is copied. When a person inherits one nonworking copy of one of these genes, every cell retains the other working copy. A tumor can form after the remaining copy is lost or disabled in a cell, causing errors to accumulate.
EPCAM has a different mechanism. Certain deletions at the 3′ end of EPCAM cause methylation and silencing of the neighboring MSH2 gene in tissues where EPCAM is active. These deletions can produce Lynch syndrome even though EPCAM itself is not a mismatch-repair protein. A complete test must be able to detect relevant deletions, not just small sequence variants. More detail is available in the EPCAM deletion test guide.
Lynch syndrome is autosomal dominant. A person with a pathogenic variant has a 50% chance of passing it to each child. Cancer is not inevitable, and risk differs substantially by gene, sex, age, family history, and environmental factors.
MLH1 and MSH2 generally confer the highest colorectal cancer risks and earlier average onset. MSH6 often produces later-onset colorectal cancer and a substantial endometrial cancer risk. PMS2 usually has lower penetrance and later onset than the other genes, though risk remains above population levels. EPCAM deletion risk depends partly on whether the deletion causes MSH2 silencing only in certain tissues.
Associated cancers can include:
- colorectal cancer;
- endometrial cancer;
- ovarian cancer;
- stomach and small-bowel cancer;
- urinary-tract cancer, especially ureter and renal pelvis;
- pancreatic and biliary-tract cancer;
- certain brain tumors;
- sebaceous skin tumors; and
- prostate cancer in some gene groups.
Not every cancer in a Lynch syndrome family is caused by the inherited variant. Common sporadic cancers still occur. Conversely, a small family or few female relatives can hide the pattern. Risk assessment should not depend only on whether three relatives had colon cancer.
The term “Lynch syndrome” should be reserved for a confirmed inherited cause or a carefully established clinical diagnosis. A tumor with mismatch-repair deficiency caused by two acquired mutations is often called a double-somatic mismatch-repair-deficient tumor, not hereditary Lynch syndrome. Distinguishing these categories prevents unnecessary lifelong surveillance and testing of relatives.
A pathogenic variant is different from a low-risk polymorphism or a variant of uncertain significance. Laboratories use evidence about population frequency, protein function, family segregation, tumor features, and published cases to classify variants. Classification can change, especially for rare missense variants.
Who should consider testing
Many Lynch syndrome diagnoses now begin with universal tumor screening. Colorectal and endometrial cancers are commonly tested for mismatch-repair protein loss or microsatellite instability regardless of age or family history. This approach finds families that older age-based criteria miss.
Germline testing is appropriate for people with:
- a colorectal or endometrial tumor showing mismatch-repair deficiency without a clear sporadic explanation;
- colorectal or endometrial cancer at a young age;
- multiple Lynch-associated primary cancers;
- a strong family pattern of colorectal, endometrial, ovarian, urinary-tract, or related cancers;
- a known Lynch syndrome variant in the family;
- a prediction-model score above a recommended threshold; or
- tumor sequencing that suggests a pathogenic mismatch-repair gene variant.
A person who is unaffected by cancer can also be tested, but the most informative first test is usually a relative who has had a Lynch-associated cancer. If that relative has a pathogenic variant, unaffected family members can receive a focused, definitive test. Testing an unaffected person first with a broad panel may produce an uninformative negative result.
Current practice often uses a hereditary cancer panel rather than a Lynch-only assay because colorectal and endometrial cancer can result from other syndromes. Panels may include APC, MUTYH, POLE, POLD1, PTEN, STK11, BRCA1, BRCA2, and additional genes. The tradeoff is a higher chance of uncertain or unexpected findings.
Testing is usually offered to adults. Predictive testing of children is generally deferred because routine Lynch syndrome surveillance begins in early adulthood, not childhood. Exceptions arise when the family history suggests very early cancer or constitutional mismatch repair deficiency.
Constitutional mismatch repair deficiency occurs when a child inherits pathogenic variants in both copies of an MMR gene, usually PMS2, MSH6, MLH1, or MSH2. It causes a severe childhood cancer predisposition involving brain tumors, blood cancers, gastrointestinal cancers, and café-au-lait-like skin findings. When both parents carry variants in the same gene, reproductive counseling is important.
A genetics appointment should document cancers on both sides of the family, ages at diagnosis, pathology, colon polyp history, ancestry, and prior testing. Death certificates and pathology records can clarify vague family reports. A “stomach cancer” remembered from decades ago may have been colon, ovarian, pancreatic, or another cancer.
People should understand possible outcomes before testing: positive, negative, uncertain, or an unexpected finding in another gene. They should also consider insurance protections and limitations in their country, especially for life, disability, or long-term-care insurance.
Tumor screening and germline testing
Tumor screening and inherited testing answer different questions. Immunohistochemistry, or IHC, looks for the presence of MLH1, PMS2, MSH2, and MSH6 proteins in tumor cells. Microsatellite instability, or MSI, measures the DNA consequence of mismatch-repair failure. Both can identify tumors likely to respond to immune checkpoint therapy and can signal possible Lynch syndrome.
The IHC loss pattern helps direct follow-up:
| Tumor IHC pattern | Common interpretation | Typical next step |
|---|---|---|
| MLH1 and PMS2 absent | MLH1 dysfunction; often sporadic methylation | MLH1 promoter methylation, and BRAF V600E in colorectal cancer where appropriate |
| MSH2 and MSH6 absent | MSH2 dysfunction or EPCAM deletion | Germline MSH2 and EPCAM analysis |
| MSH6 absent alone | MSH6 dysfunction | Germline MSH6 testing |
| PMS2 absent alone | PMS2 dysfunction, sometimes MLH1 alteration | Germline PMS2 with careful method; consider MLH1 if needed |
| All four retained | MMR-proficient tumor | Lynch less likely, but germline testing may still be indicated by history |
The proteins work in pairs. MLH1 stabilizes PMS2, so MLH1 loss usually removes both. MSH2 stabilizes MSH6, so MSH2 loss usually removes both. Isolated PMS2 or MSH6 loss points more directly to that partner, though staining artifacts and unusual variants can complicate the pattern.
Loss of MLH1 and PMS2 is frequently sporadic. Acquired methylation of the MLH1 promoter silences the gene in the tumor. In colorectal cancer, BRAF V600E strongly supports a sporadic pathway because it is uncommon in Lynch-associated colorectal cancer. BRAF is not an adequate substitute for methylation testing in endometrial cancer.
A methylated tumor is usually sporadic, but exceptions exist. Constitutional MLH1 epimutation is rare, and some people with germline MLH1 variants can develop a methylated tumor. Young age, multiple cancers, or a strong family history may justify genetics evaluation despite methylation.
Germline testing uses blood or saliva and should include sequencing plus deletion/duplication analysis. PMS2 is technically challenging because nearby pseudogenes resemble it. Validated laboratories use long-range PCR, specialized NGS, or reflex methods to avoid assigning a pseudogene variant to PMS2. EPCAM analysis must cover deletions capable of silencing MSH2.
Paired tumor-normal sequencing can be very helpful when germline testing is negative but the tumor is mismatch-repair deficient. Finding two acquired hits in the same MMR gene can explain a double-somatic tumor. It can also uncover a missed germline variant, loss of heterozygosity, or another mechanism. Tumor-only sequencing cannot reliably distinguish inherited from acquired findings.
MSI and IHC are highly concordant but not identical. MSH6-deficient tumors can show lower levels of instability, and technical factors can affect both tests. When morphology, family history, and results conflict, repeat testing or pathology review is appropriate.
A person with cancer can begin germline testing before all tumor triage is complete when the history is strongly suggestive or when treatment decisions are urgent. Testing pathways should avoid losing patients between multiple sequential steps.
How to interpret results
A pathogenic or likely pathogenic variant confirms Lynch syndrome when found in MLH1, MSH2, MSH6, PMS2, or a qualifying EPCAM deletion. “Likely pathogenic” is managed like pathogenic because the evidence for disease causation is strong. The report should name the gene, DNA change, protein effect, and classification.
A positive result does not mean cancer is present. It means future risk is increased and surveillance should follow gene-specific guidance. A person already treated for one cancer also remains at risk for a second primary cancer.
A true negative occurs when the family’s pathogenic variant is known and the tested relative does not carry it. That person usually does not have the family’s Lynch syndrome risk and cannot pass that variant to children. Screening can often return to population recommendations, adjusted for any independent personal or family history.
An uninformative negative occurs when no familial pathogenic variant has been established. It does not erase a strong history. The family’s cancers may result from a variant the test could not detect, another gene, shared exposures, or chance. Management may still be based on family history.
A variant of uncertain significance, or VUS, does not confirm Lynch syndrome. It should not lead to preventive hysterectomy, shortened colonoscopy intervals solely because of the variant, or predictive testing of healthy relatives. Relatives may occasionally be studied through a laboratory segregation program, but that is different from clinical cascade testing.
An unexpected positive in another gene may be found on a panel. Management should follow the evidence for that gene rather than applying Lynch syndrome recommendations. Some moderate-risk genes do not justify the same intensity of screening.
When germline testing is negative and tumor testing shows two somatic MMR hits, relatives usually do not need testing for those tumor-only variants. The patient may still need surveillance based on cancer history, but the family does not automatically inherit the same risk.
Mosaicism is uncommon but possible. A pathogenic variant present in only a fraction of blood cells may be constitutional mosaicism or clonal hematopoiesis. Testing another tissue and reviewing VAF can clarify the origin. A low-level MSH6 or TP53 result in blood after chemotherapy deserves careful evaluation.
A result can be reclassified. The testing laboratory should have current contact information, and the patient should keep a copy of the report. Genetics clinics can periodically review an unresolved VUS, especially if new cancers arise in the family.
Screening and risk reduction
Colonoscopy is the central preventive measure. It removes precancerous polyps and can detect early cancer. Recommended starting age and interval depend on the gene and family history. MLH1 and MSH2 carriers commonly begin in their early 20s to mid-20s and repeat every 1 to 2 years. MSH6 and PMS2 carriers may begin later, often around age 30 to 35, unless the family had earlier cancer. Exact guidance differs by organization and should be individualized.
Lynch-associated cancers can develop between examinations, so a 10-year population interval is not appropriate for a confirmed carrier. High-quality preparation, cecal intubation, adequate withdrawal time, and complete polyp removal matter. Colonoscopy remains necessary even after a negative stool test.
Endometrial cancer often presents with abnormal uterine bleeding. Carriers should report any bleeding after menopause, bleeding between periods, or major cycle changes promptly. Screening with transvaginal ultrasound or endometrial biopsy has not been proven to reduce mortality, though periodic biopsy may be considered in some programs. Education about symptoms is essential.
Risk-reducing hysterectomy with removal of the fallopian tubes, with or without ovaries depending on gene and age, can be considered after childbearing. The timing should reflect the gene-specific endometrial and ovarian risks, menopause consequences, family history, and personal preferences. PMS2 ovarian cancer risk appears low enough that automatic ovary removal may not be justified solely for the variant.
Aspirin can reduce colorectal cancer incidence in Lynch syndrome, but the optimal dose and duration continue to be studied. Decisions should consider ulcer history, bleeding risk, anticoagulants, kidney disease, age, and cardiovascular factors. Aspirin should not be started solely from an online recommendation.
Upper endoscopy may be considered based on gene, ancestry, family history, local gastric cancer incidence, and Helicobacter pylori status. Urinary-tract surveillance, pancreatic screening, prostate screening, and skin examination are more selective because evidence is less certain or risk is gene-dependent.
Pancreatic screening is generally reserved for carriers with a relevant family history and should occur at experienced centers using MRI/MRCP and/or endoscopic ultrasound. Routine screening of every carrier is not universally recommended.
After colorectal cancer, the extent of colon surgery depends on age, gene, tumor location, bowel function, and future cancer risk. More extensive colectomy lowers the chance of a second colorectal cancer but can affect quality of life. A positive genetic result before surgery can therefore influence the operation.
Healthy habits do not remove inherited risk but still matter. Avoiding tobacco, maintaining a healthy weight, exercising, limiting alcohol, and managing blood pressure improve overall health and may lower risk. They complement rather than replace surveillance.
Family testing and reproductive options
Once a pathogenic variant is identified, adult first-degree relatives should be offered cascade testing for that exact variant. Parents, siblings, and children each have a 50% chance of carrying it. Testing can then move outward to aunts, uncles, cousins, nieces, and nephews through the side of the family where the variant is found.
A copy of the laboratory report is the most useful document to share. A family letter can explain the gene, variant, inheritance pattern, and how relatives can obtain counseling. Describing the result as “a colon cancer gene” is not enough because laboratories need the exact notation.
Relatives who test positive enter gene-specific surveillance. Those who test negative for the known family variant generally avoid intensive Lynch syndrome screening. This ability to separate higher-risk from average-risk relatives is one of the main benefits of finding the familial cause.
Children are not usually tested because medical management seldom changes before adulthood. Families can begin discussing the result gradually and arrange counseling before surveillance should start. Earlier testing may be considered if cancers occurred unusually young or constitutional mismatch repair deficiency is a concern.
Reproductive options include natural conception, prenatal diagnosis, use of donor eggs or sperm, adoption, and in vitro fertilization with preimplantation genetic testing for monogenic disease. These are personal choices. Genetic counseling should explain success rates, cost, timing, and the possibility of embryos with inconclusive results.
When both partners carry pathogenic variants in the same mismatch-repair gene, each pregnancy can have a 25% chance of constitutional mismatch repair deficiency. Partner testing is not needed for every Lynch syndrome carrier, but it may be considered for consanguinity, shared ancestry, a PMS2 variant with higher carrier frequency, or a suggestive partner history.
A person’s result also identifies which side of the family is at risk. Testing parents can clarify this when both are available. If neither parent carries the variant, it may be de novo or due to parental mosaicism; siblings may still have a small residual risk.
Family communication can be difficult. Genetics clinics may provide letters, telehealth visits, or testing programs for relatives in other regions. Privacy laws often prevent clinicians from contacting relatives directly without permission, so the patient’s participation is important.
Treatment, privacy, and next steps
Mismatch-repair deficiency and MSI-high status can guide immune checkpoint treatment in several cancers. This is a tumor biomarker use and can apply whether the cause is Lynch syndrome or a sporadic tumor. A germline result adds inherited-risk information but does not by itself establish that every future tumor will be MSI-high.
For a new colorectal or endometrial cancer, ask whether tumor IHC or MSI was performed and obtain the full report. For MLH1/PMS2 loss, ask whether MLH1 methylation was tested and whether the result fits the age and family history. For MSH2/MSH6 loss, confirm that EPCAM deletion analysis is included.
Before germline testing, ask:
- Is this a focused family-variant test or a broader panel?
- Does the laboratory reliably analyze PMS2 and EPCAM deletions?
- What will a negative result mean in this family?
- How will a VUS be managed and updated?
- Which screening recommendations apply to the specific gene?
- Should testing affect planned colorectal or gynecologic surgery?
- What privacy and insurance protections apply locally?
- How can relatives access cascade testing?
After a positive result, establish a written surveillance plan with start ages and intervals. The plan should name who coordinates colonoscopy, gynecologic care, and any selective screening. Update it as guidelines and family history change.
After an uninformative negative result, do not discard the family history. Ask whether tumor testing, paired tumor-normal analysis, updated panel testing, or testing another affected relative could clarify the cause. Older tests may not have included deletion analysis, EPCAM, or newer genes.
After a VUS, avoid irreversible actions based solely on the uncertain finding. Management should follow personal and family history. Contact the laboratory or genetics clinic if the variant is reclassified.
Genetic information can affect emotional well-being and family relationships. Some people feel relief from having an explanation; others feel guilt or fear. Counseling and patient support groups can help. The purpose of testing is not to predict an unavoidable future but to create opportunities for prevention, early detection, informed treatment, and precise family testing.
References
- Lynch Syndrome 2021 (GeneReview)
- Diagnosis and management of Lynch syndrome 2022 (Review)
- Canadian consensus for the assessment and testing of Lynch syndrome 2025 (Consensus)
- Cancer risks in Lynch syndrome carriers: a systematic review and meta-analysis 2025 (Systematic Review)
- Evaluating colonoscopy screening intervals in patients with Lynch syndrome 2023 (Cohort Study)
- Screening and risk reducing surgery for endometrial or ovarian cancers in Lynch syndrome: a systematic review 2022 (Systematic Review)
Disclaimer
This article is educational and does not replace genetic counseling, individualized cancer-risk assessment, or medical care. Surveillance and risk-reducing surgery should be based on the specific gene, personal history, family history, age, and current guidelines. New rectal bleeding, unexplained anemia, postmenopausal bleeding, or other concerning symptoms require medical evaluation rather than waiting for routine screening.
