Immunohistochemistry screening (IHC)
IHC screening looks to see if certain proteins are absent in the tumor sample, indicating that one of the Lynch syndrome genes might not be working properly. Lynch syndrome mutations affect whether the MLHL, MSH2, MSH6, and PMS2 proteins are made and located in the correct place.
| Test Result | What it means | Next Step |
|---|---|---|
| Absent MLH1 and PMS2 proteins | Test could not determine if you are likely to have Lynch syndrome | Further testing needed |
| Absent MSH2 and MSH6 proteins | You are likely to have Lynch syndrome | Genetic counseling and testing |
| Absent MSH6 protein | You are likely to have Lynch syndrome | Genetic counseling and testing |
| Absent PMS2 protein | You are likely to have Lynch syndrome | Genetic counseling and testing |
| All 4 proteins present | You are unlikely to have Lynch syndrome | No additional testing is needed, unless you have a strong family history of colorectal cancer, or had colorectal cancer before age 50 |