microsatellite instability-low
Also written as: MSI-L — microsatellite instability-low
A tumor phenotype characterized by low-level defects in DNA mismatch repair, falling between microsatellite stable and microsatellite instability-high classifications.
Full Definition
Microsatellite instability-low (MSI-L) represents an intermediate category of DNA mismatch repair deficiency where tumors exhibit some microsatellite alterations but do not meet the threshold for MSI-high classification. This classification has uncertain clinical significance in precision oncology, as MSI-L tumors typically do not respond to immune checkpoint inhibitors like MSI-high tumors do. The designation requires careful interpretation in clinical reports, as treatment implications differ significantly from MSI-high tumors. Most guidelines focus primarily on MSI-high vs. microsatellite stable classifications for therapeutic decision-making.
Usage
Usage note: Hyphenate when used as a compound adjective; avoid confusion with MSI-H in clinical contexts.
In Context
- "The tumor was classified as microsatellite instability-low, indicating uncertain benefit from immunotherapy." — precision oncology report
- "Editorial note: Distinguish clearly between MSI-L and MSI-H when discussing immunotherapy eligibility." — clinical guideline document