# MSI-high (microsatellite instability by PCR or sequencing)

Source: https://onco.cc/biomarkers/msi-high/  
OnCo record `msi-high` (Biomarker). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

MSI-high means the tumour's DNA has unstable repeat sequences, the footprint of failed mismatch repair. It is measured by PCR or sequencing, gives the same answer as dMMR in most tumours, and unlocks the same immunotherapies.

## Summary

Microsatellite instability is scored by PCR across a panel of mononucleotide repeats (MSI-H when a set fraction of markers is unstable, typically 2 of 5 Bethesda or Promega markers, or 30 percent or more of a larger panel) or by next-generation sequencing algorithms that count unstable loci across hundreds of sites; MSS is stable and MSI-L is intermediate and grouped with MSS. Labels write 'MSI-H or dMMR' and accept either route; FoundationOne CDx and Caris MI Cancer Seek carry MSI-H companion claims for pembrolizumab and dostarlimab, the Biocartis Idylla MSI test for nivolumab in colorectal cancer, and, in the other direction, the Promega OncoMate MSI and Caris assays report 'not MSI-H' to select pembrolizumab with lenvatinib in endometrial cancer.

## Fields

- Kind: Biomarker
- Last checked: 2026-09-23
- Also known as: MSI-H; MSI-high; MSI high; microsatellite instability-high; microsatellite unstable; MSI status; MSI-H/dMMR; MSS; microsatellite stable
- Tags: biomarker; mmr

## Sources

- KEYTRUDA prescribing information (DailyMed): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9333c79b-d487-4538-a9f0-71b91a02b287
- OPDIVO prescribing information (DailyMed): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f570b9c4-6846-4de2-abfa-4d0a4ae4e394

## Connected records

- biomarkers: [dMMR (mismatch repair deficiency by IHC)](https://onco.cc/biomarkers/dmmr-ihc/), [TMB-high (tumour mutational burden >= 10 mutations per megabase)](https://onco.cc/biomarkers/tmb-high/)
- cancers: [Colorectal cancer](https://onco.cc/cancers/colorectal/), [Endometrial cancer](https://onco.cc/cancers/endometrial/), [Metastatic cancer (cancer that has spread)](https://onco.cc/cancers/metastatic-cancer/), [Microsatellite-unstable (MSI-high) gastric cancer](https://onco.cc/cancers/gastric-msi-high/), [Mismatch-repair-deficient endometrial cancer](https://onco.cc/cancers/endometrial-mmr-deficient/)
- drugs: [Dostarlimab](https://onco.cc/drugs/dostarlimab/), [FoundationOne CDx / Liquid CDx](https://onco.cc/drugs/foundationone-cdx/), [Ipilimumab](https://onco.cc/drugs/ipilimumab/), [Lenvatinib](https://onco.cc/drugs/lenvatinib/), [MI Cancer Seek](https://onco.cc/drugs/caris-mi-cancer-seek/), [Nivolumab](https://onco.cc/drugs/nivolumab/), [Pembrolizumab](https://onco.cc/drugs/pembrolizumab/)
- terms: [Microsatellite instability (MSI-H) / mismatch repair deficiency (dMMR)](https://onco.cc/terms/msi/), [Microsatellite-stable (MSS) / mismatch-repair proficient (pMMR)](https://onco.cc/terms/mss-pmmr/), [Next-generation sequencing (NGS)](https://onco.cc/terms/ngs/), [Tumour-agnostic (tissue-agnostic) approval](https://onco.cc/terms/tumour-agnostic/)
- targets: [Mismatch repair proteins (MLH1, MSH2, MSH6, PMS2)](https://onco.cc/targets/mmr/)

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JSON: https://onco.cc/api/v1/entities/msi-high.json