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.See related research by Sveen et al. 10.1186/s13073-017-0434-0.