Dissecting microsatellite instability in colorectal cancer: One size does not fit all

Microsatellite instability (MSI) marks distinct subsets of tumors in many cancer types and is caused by mutations in genes required for mismatch repair. A recent report analyses the molecular foundations of MSI-positive colorectal cancers and reveals substantial molecular heterogeneity, which might have consequences for the potential use of immunotherapy in MSI-positive cancers.