Short answer
Lynch syndrome is an inherited cancer-risk syndrome most strongly linked with colorectal and endometrial cancer, though other cancers can be involved. Testing often starts with tumor screening in someone who has cancer, then germline genetic testing to see whether the change is inherited and relevant to relatives. The usual genes include MLH1, MSH2, MSH6, PMS2, and EPCAM.
Testing steps
| Step | What it answers | Limit |
|---|---|---|
| Family history review | Looks for early, repeated, or related cancers in relatives. | Small families, adoption, and missing records can hide risk. |
| Tumor testing | Can show mismatch repair or microsatellite instability patterns in a cancer. | Abnormal tumor results do not always mean inherited Lynch syndrome. |
| Germline genetic testing | Checks whether a Lynch-related variant is present in inherited DNA. | May find a VUS or may not explain a strong family history. |
| Cascade testing | Tests relatives for a known family variant. | Most useful when the family's specific pathogenic variant is known. |
What tumor screening can and cannot tell you
CDC and NCI both emphasize that abnormal tumor screening can point toward Lynch syndrome, but it does not by itself prove the change is inherited. That is why the same person may need both tumor review and germline testing. A germline positive result can change screening for the person and relatives; a germline negative result does not always erase concern if the tumor result is still suspicious or the family history is strong.
If a pathogenic variant is confirmed, family follow-up often becomes cascade testing: targeted testing for the same specific change in parents, siblings, children, and sometimes more distant relatives.
Why counseling matters
A positive Lynch syndrome result can change colonoscopy timing, gynecologic risk discussions, and sometimes screening for other cancers. A negative result is not always simple if no affected relative was tested first or if a tumor result was abnormal for non-inherited reasons. Genetic counseling helps connect the test result to the person, relatives, and medical plan, and CDC's cascade-testing materials are a useful next step when a family variant is known.
When family history changes the next step
Follow-up matters more when tumor screening is abnormal, when the family history of colon, endometrial, or related cancers is stronger than the report alone, or when relatives may need cascade testing. Genetics counseling helps decide whether the next step is germline testing, tumor review, or both.
Questions to ask
- Was the test done on tumor tissue, blood or saliva germline DNA, or both?
- Which genes were included, such as MLH1, MSH2, MSH6, PMS2, or EPCAM?
- If the result is negative, does it actually rule out the family concern?
- Which relatives should consider targeted testing or earlier screening?
- Would a cascade-testing letter or family letter help relatives get the right test?
FAQ
What does Lynch syndrome genetic testing look for?
It looks for inherited changes in mismatch repair genes such as MLH1, MSH2, MSH6, PMS2, or EPCAM that can raise cancer risk for the person and relatives.
Is tumor screening the same as germline testing?
No. Tumor screening looks at the cancer tissue, while germline testing looks for inherited DNA changes in blood, saliva, or another normal sample.
Which genes are usually involved?
The classic Lynch syndrome genes are MLH1, MSH2, MSH6, PMS2, and EPCAM, although the exact panel can vary by lab and clinical situation.
Does a negative result rule out Lynch syndrome?
Not always. A negative result can still leave family-history concern, incomplete tumor follow-up, or a variant not covered by the test.
Who should be tested first when possible?
When possible, testing should start with the relative who has had cancer, because that often gives the clearest answer for the family.
Why is genetic counseling useful?
Counseling helps connect the result to colon, endometrial, ovarian, and other cancer screening, plus whether relatives should have cascade testing.
Related guides: hereditary cancer genetic testing, BRCA testing vs broad cancer panels, when to use a genetic counselor, and tumor genomic vs inherited testing.