MSI-H
Pronunciation: M-S-I-high
Also written as: MSI-H — Microsatellite Instability-High
Microsatellite Instability-High, a genomic phenotype indicating defective DNA mismatch repair.
Full Definition
MSI-H (Microsatellite Instability-High) describes tumors with a high level of microsatellite instability, typically resulting from defective DNA mismatch repair mechanisms. MSI-H tumors accumulate insertion-deletion mutations in repetitive DNA sequences called microsatellites. This phenotype is strongly associated with response to immune checkpoint inhibitors and serves as an FDA-approved biomarker for immunotherapy across multiple cancer types. Editors must distinguish MSI-H from MSI-stable (MSS) and understand that MSI-H testing can be performed through PCR-based assays, immunohistochemistry, or next-generation sequencing approaches.
Usage
Usage note: Always hyphenate (MSI-H, not MSI H). Distinguish clearly from related terms like dMMR (deficient mismatch repair).
In Context
- "The colorectal tumor demonstrated MSI-H status by PCR analysis of five microsatellite markers." — molecular pathology report
- "MSI-H tumors showed a 40% response rate to PD-1 inhibitor therapy in this cohort." — clinical trial manuscript