Microsatellite Instability in Colorectal Cancers by Race and Hispanic Ethnicity Group

Microsatellite instability (MSI) is found in nearly all Lynch syndrome colorectal cancers and in about half of serrated pathway cancers. Because serrated pathway cancer is more common, it produces about 80% of all microsatellite-unstable tumors. Current recommendations are to screen all colorectal cancers for MSI or failed expression of mismatch repair proteins. Positive tests for MSI or failure to express mismatch repair protein MLH1 should be followed by BRAF mutation tests or hypermethylation assays to distinguish MSI arising through the Lynch pathway from MSI arising through the serrated pathway.

In the current study, researchers tested 253 surgically resected colorectal cancer specimens for failed expression of mismatch repair proteins,…