microsatellite instability
Also written as: MSI — Microsatellite Instability
A molecular phenotype indicating defective DNA mismatch repair mechanisms in tumor cells.
Full Definition
Microsatellite instability (MSI) is a molecular phenotype characterized by widespread alterations in the length of microsatellite sequences due to defective DNA mismatch repair (MMR) systems. MSI-high tumors typically exhibit increased mutation rates and enhanced immunogenicity, making them more responsive to immunotherapy treatments. MSI testing has become a standard biomarker for treatment selection in colorectal, endometrial, and other cancer types, with specific guidelines for testing methodologies and interpretation.
Usage
Usage note: Results typically reported as MSI-high, MSI-low, or microsatellite stable (MSS).
In Context
- "Microsatellite instability testing revealed MSI-high status, indicating the patient's eligibility for pembrolizumab therapy." — Pathology report
- "The laboratory reported microsatellite instability results using both PCR and immunohistochemistry methods." — Clinical documentation