An immunohistochemistry (IHC) test looks for missing proteins in tumor cells. The premise behind the test is that if the MMR genes are working properly, their protein products should be present in the tumor. However, if there is a mutation in one of the Lynch syndrome MMR genes, that gene’s protein will be absent in the tumor.
83-90% of Lynch-related tumors and 20% of sporadic tumors have at least one of these proteins absent.
IHC testing looks to see if a tumor is missing any of the MMR proteins. If any of the MMR proteins are missing, the test is abnormal, and you are more likely to have Lynch syndrome. To find out if you have Lynch syndrome, you need to do a genetic test to check for specific genes.
If the test is normal, you are less likely to have Lynch syndrome, but it cannot be ruled out entirely.
