microsatellite instability
Pronunciation: MY-kroh-sat-uh-lite in-stuh-BIL-i-tee
A molecular phenotype characterized by accumulated mutations in repetitive DNA sequences, indicating defective DNA mismatch repair.
Full Definition
Microsatellite instability (MSI) results from deficient mismatch repair (dMMR) mechanisms, leading to hypermutation phenotype particularly relevant in colorectal and gastric cancers. MSI-high tumors demonstrate distinct clinical behavior, including better prognosis in early-stage disease and enhanced response to immune checkpoint inhibitors. Testing methodology includes PCR-based analysis or immunohistochemistry for mismatch repair proteins (MLH1, MSH2, MSH6, PMS2). Editorial precision is required when reporting MSI status classifications (MSI-high, MSI-low, microsatellite stable).
Usage
Usage note: Hyphenate compound descriptors (MSI-high, MSI-low); distinguish from mismatch repair deficiency terminology.
In Context
- "Tumor testing revealed microsatellite instability-high status with loss of MLH1 expression." — Molecular pathology report
- "Patients with MSI-high tumors showed remarkable response to pembrolizumab therapy." — Clinical trial publication