microsatellite instability
A molecular phenotype resulting from defective DNA mismatch repair, characterized by length variations in repetitive DNA sequences.
Full Definition
Microsatellite instability (MSI) is a hypermutable phenotype that occurs when DNA mismatch repair systems fail to function properly. This condition is characterized by alterations in the length of microsatellite sequences—short repetitive DNA motifs—throughout the genome. MSI is commonly observed in colorectal and endometrial cancers and serves as both a diagnostic marker and a predictor of response to immune checkpoint inhibitors. Tumors with high levels of microsatellite instability (MSI-H) typically show increased immunogenicity due to the production of numerous frameshift mutations and resulting neoantigens.
Usage
Usage note: Abbreviate as MSI after first use; distinguish between MSI-H (high) and MSI-L (low) classifications.
In Context
- "The pathology report confirmed microsatellite instability-high status in the colorectal adenocarcinoma." — Diagnostic report
- "Patients with microsatellite instability showed enhanced response to anti-PD-1 therapy." — Clinical trial publication