Microsatellite Instability (MSI) screening
MSI screening is used to see if the Lynch syndrome genes are working properly. Microsatellites are regions of repeated DNA that change in length (show instability) when mismatch repair is not working properly. MSI testing looks at the length of certain DNA microsatellites from the tumor sample to see if they have gotten longer or shorter as a measure of instability.
| Test Result | What it means | Next Step |
|---|---|---|
| MSI high (MSI-H) | You are likely to have Lynch syndrome | Genetic counseling and testing |
| MSI low (MSI-L) | The test could not determine if you are likely to have Lynch syndrome | Genetic counseling and testing |
| MSI stable (MSI-S) | You are unlikely to have Lynch syndrome | No genetic counseling is needed, unless you have a strong family history of colorectal cancer, or had colorectal cancer before age 50 |