microsatellite instability-high
Also written as: MSI-H — Microsatellite Instability-High
A tumor phenotype characterized by widespread mutations in repetitive DNA sequences, predictive of immunotherapy response.
Full Definition
Microsatellite instability-high (MSI-H) is a molecular phenotype resulting from defective DNA mismatch repair mechanisms, leading to accumulation of mutations in repetitive DNA sequences called microsatellites. MSI-H tumors are characterized by high mutational burden and increased neoantigen expression, making them highly responsive to immune checkpoint inhibitors. This phenotype is found in approximately 15% of colorectal cancers, 30% of endometrial cancers, and smaller percentages of other tumor types. MSI-H testing has become standard for guiding immunotherapy decisions across multiple cancer types.
Usage
Usage note: Abbreviate as MSI-H; hyphenate when used as compound modifier.
In Context
- "Tumor testing revealed microsatellite instability-high status." — molecular pathology report
- "The MSI-H phenotype predicted excellent response to pembrolizumab." — treatment response note