Intermediate
Technical
In the Industry Vocabulary Test
microsatellite instability
A genomic phenotype characterized by widespread mutations in repetitive DNA sequences due to defective mismatch repair.
Full Definition
Microsatellite instability (MSI) occurs when cells lose the ability to repair DNA mismatches, leading to accumulation of mutations in short tandem repeat sequences throughout the genome. This phenotype is caused by deficiencies in mismatch repair genes (MLH1, MSH2, MSH6, PMS2) and results in a hypermutated tumor profile. MSI status is a critical biomarker for immunotherapy response, as MSI-high tumors typically respond well to immune checkpoint inhibitors due to their high neoantigen burden.
Usage
Usage note: Distinguish from the abbreviation MSI-H (microsatellite instability-high), which refers to the severity classification.
In Context
- "The tumor demonstrated microsatellite instability, making the patient eligible for pembrolizumab therapy." — Pathology report
- "Microsatellite instability testing is now standard for all colorectal cancer diagnoses." — Clinical guideline
Also known as
MSI
Contrasted with
microsatellite stable
MSS
Don't confuse with
mismatch repair deficiency
MSI-H