{"entity":{"id":"msi-high","kind":"biomarker","name":"MSI-high (microsatellite instability by PCR or sequencing)","aka":["MSI-H","MSI-high","MSI high","microsatellite instability-high","microsatellite unstable","MSI status","MSI-H/dMMR","MSS","microsatellite stable"],"tldr":"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.","asOf":"2026-09-23","links":[{"label":"KEYTRUDA prescribing information (DailyMed)","url":"https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9333c79b-d487-4538-a9f0-71b91a02b287"},{"label":"OPDIVO prescribing information (DailyMed)","url":"https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f570b9c4-6846-4de2-abfa-4d0a4ae4e394"}],"tags":["biomarker","mmr"],"related":["dmmr-ihc","tmb-high"],"cancers":["colorectal","endometrial","endometrial-mmr-deficient","gastric-msi-high","metastatic-cancer"],"sections":[],"technologies":[],"targets":[],"drugs":["pembrolizumab","nivolumab","ipilimumab","dostarlimab","lenvatinib","foundationone-cdx","caris-mi-cancer-seek"],"companies":[],"institutions":[],"pathways":[],"terms":["msi","mss-pmmr","ngs","tumour-agnostic"],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"target":"mmr","measurement":"msi-status","scoringRule":{"text":"MSI-H: instability at the required fraction of tested microsatellite loci (for example 2 or more of 5 mononucleotide markers by PCR, or the sequencing panel's validated cut-off across many loci); otherwise microsatellite stable.","quote":"Microsatellite instability – High (MSI-H)","source":"https://www.fda.gov/medical-devices/in-vitro-diagnostics/list-cleared-or-approved-companion-diagnostic-devices-in-vitro-and-imaging-tools","sourceLabel":"FDA: List of FDA-Authorized Companion Diagnostic Devices"},"thresholds":[{"value":"MSI-H or dMMR, tumour-agnostic","drugId":"pembrolizumab","cancerId":"metastatic-cancer","regulator":"FDA","source":"https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9333c79b-d487-4538-a9f0-71b91a02b287","quote":"unresectable or metastatic microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) solid tumors, as determined by an FDA-authorized test, that have progressed following prior treatment and who have no satisfactory alternative treatment options.","status":"current"},{"value":"MSI-H or dMMR","drugId":"pembrolizumab","cancerId":"colorectal","regulator":"FDA","source":"https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9333c79b-d487-4538-a9f0-71b91a02b287","quote":"for the treatment of patients with unresectable or metastatic MSI-H or dMMR colorectal cancer (CRC) as determined by an FDA-authorized test.","status":"current"},{"value":"MSI-H or dMMR (single agent after chemotherapy)","drugId":"nivolumab","cancerId":"colorectal","regulator":"FDA","source":"https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f570b9c4-6846-4de2-abfa-4d0a4ae4e394","quote":"OPDIVO, as a single agent, is indicated for the treatment of adult and pediatric patients 12 years and older with microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) metastatic colorectal cancer (CRC) that has progressed following treatment with a fluoropyrimidine, oxaliplatin, and irinotecan.","status":"current"},{"value":"Not MSI-H / pMMR (selects the lenvatinib combination)","drugId":"lenvatinib","cancerId":"endometrial","regulator":"FDA","source":"https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9333c79b-d487-4538-a9f0-71b91a02b287","quote":"KEYTRUDA, in combination with lenvatinib, is indicated for the treatment of adult patients with advanced endometrial carcinoma that is mismatch repair proficient (pMMR) or not MSI-H as determined by an FDA-authorized test","status":"current"}],"tests":["foundationone-cdx","foundationone-liquid-cdx","caris-mi-cancer-seek","tempus-xt","trusight-oncology-500","stratangs","omniseq-insight","altera","oncoextra","bostongene-tumor-portrait"],"assays":["msi-pcr","foundationone-cdx-panel"],"companionDiagnostics":[{"device":"FoundationOne CDx","maker":"Foundation Medicine","companyId":"foundation-medicine","drugs":["pembrolizumab"],"indication":"Solid Tumors - Tissue","pma":"P170019/S029 (02/18/2022)","source":"https://www.fda.gov/medical-devices/in-vitro-diagnostics/list-cleared-or-approved-companion-diagnostic-devices-in-vitro-and-imaging-tools"},{"device":"MI Cancer Seek (MCS)","maker":"Caris Life Sciences","companyId":"caris","drugs":["pembrolizumab"],"indication":"Solid Tumors - Tissue","pma":"P240010 (11/05/2024)","source":"https://www.fda.gov/medical-devices/in-vitro-diagnostics/list-cleared-or-approved-companion-diagnostic-devices-in-vitro-and-imaging-tools"},{"device":"MI Cancer Seek (MCS)","maker":"Caris Life Sciences","companyId":"caris","drugs":["dostarlimab"],"indication":"Solid Tumors - Tissue","pma":"P240010 (11/05/2024)","source":"https://www.fda.gov/medical-devices/in-vitro-diagnostics/list-cleared-or-approved-companion-diagnostic-devices-in-vitro-and-imaging-tools"},{"device":"Idylla CDx MSI Test","maker":"Biocartis","drugs":["nivolumab","ipilimumab"],"indication":"Colorectal Cancer (CRC) - Tissue","pma":"P250005 (08/15/2025)","source":"https://www.fda.gov/medical-devices/in-vitro-diagnostics/list-cleared-or-approved-companion-diagnostic-devices-in-vitro-and-imaging-tools"},{"device":"OncoMate MSI Dx Analysis System","maker":"Promega","drugs":["pembrolizumab","lenvatinib"],"indication":"Endometrial Carcinoma (EC) - Tissue","pma":"P240026 (11/05/2025)","source":"https://www.fda.gov/medical-devices/in-vitro-diagnostics/list-cleared-or-approved-companion-diagnostic-devices-in-vitro-and-imaging-tools"}],"forPatient":"MSI-high on a PCR or sequencing report means the same for treatment as dMMR on a stain: checkpoint immunotherapy is on label across many cancers once other treatment has been tried, and first line in bowel cancer. A stable (MSS) result in endometrial cancer selects a different combination, pembrolizumab with lenvatinib. Either result should prompt a conversation about inherited risk."},"route":"/biomarkers/msi-high/","neighbours":{"biomarker":[{"id":"dmmr-ihc","kind":"biomarker","name":"dMMR (mismatch repair deficiency by IHC)","route":"/biomarkers/dmmr-ihc/"},{"id":"tmb-high","kind":"biomarker","name":"TMB-high (tumour mutational burden >= 10 mutations per megabase)","route":"/biomarkers/tmb-high/"}],"cancer":[{"id":"colorectal","kind":"cancer","name":"Colorectal cancer","route":"/cancers/colorectal/"},{"id":"endometrial","kind":"cancer","name":"Endometrial cancer","route":"/cancers/endometrial/"},{"id":"metastatic-cancer","kind":"cancer","name":"Metastatic cancer (cancer that has spread)","route":"/cancers/metastatic-cancer/"},{"id":"gastric-msi-high","kind":"cancer","name":"Microsatellite-unstable (MSI-high) gastric cancer","route":"/cancers/gastric-msi-high/"},{"id":"endometrial-mmr-deficient","kind":"cancer","name":"Mismatch-repair-deficient endometrial cancer","route":"/cancers/endometrial-mmr-deficient/"}],"drug":[{"id":"dostarlimab","kind":"drug","name":"Dostarlimab","route":"/drugs/dostarlimab/"},{"id":"foundationone-cdx","kind":"drug","name":"FoundationOne CDx / Liquid CDx","route":"/drugs/foundationone-cdx/"},{"id":"ipilimumab","kind":"drug","name":"Ipilimumab","route":"/drugs/ipilimumab/"},{"id":"lenvatinib","kind":"drug","name":"Lenvatinib","route":"/drugs/lenvatinib/"},{"id":"caris-mi-cancer-seek","kind":"drug","name":"MI Cancer Seek","route":"/drugs/caris-mi-cancer-seek/"},{"id":"nivolumab","kind":"drug","name":"Nivolumab","route":"/drugs/nivolumab/"},{"id":"pembrolizumab","kind":"drug","name":"Pembrolizumab","route":"/drugs/pembrolizumab/"}],"term":[{"id":"msi","kind":"term","name":"Microsatellite instability (MSI-H) / mismatch repair deficiency (dMMR)","route":"/terms/msi/"},{"id":"mss-pmmr","kind":"term","name":"Microsatellite-stable (MSS) / mismatch-repair proficient (pMMR)","route":"/terms/mss-pmmr/"},{"id":"ngs","kind":"term","name":"Next-generation sequencing (NGS)","route":"/terms/ngs/"},{"id":"tumour-agnostic","kind":"term","name":"Tumour-agnostic (tissue-agnostic) approval","route":"/terms/tumour-agnostic/"}],"target":[{"id":"mmr","kind":"target","name":"Mismatch repair proteins (MLH1, MSH2, MSH6, PMS2)","route":"/targets/mmr/"}]}}