# dMMR (mismatch repair deficiency by IHC)

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

## TL;DR

dMMR means one of the four mismatch repair proteins is missing from the tumour cell nuclei on a stain. It is the tissue-level twin of MSI-high and opens checkpoint immunotherapy in endometrial, bowel and many other cancers.

## Summary

Immunohistochemistry for MLH1, PMS2, MSH2 and MSH6 is read as retained or lost nuclear staining in tumour cells against an internal positive control; loss of any protein is mismatch repair deficient. Paired losses (MLH1 with PMS2, MSH2 with MSH6) reflect the heterodimers. Labels for pembrolizumab (tumour-agnostic, colorectal, endometrial), dostarlimab (endometrial and tumour-agnostic), nivolumab and ipilimumab (colorectal) and durvalumab (endometrial with chemotherapy) use 'MSI-H or dMMR' and name FDA-authorised tests; the VENTANA MMR RxDx Panel and the Agilent MMR IHC Panel pharmDx are the listed companion diagnostics. The dostarlimab label advises testing the primary tumour before temozolomide in gliomas because chemotherapy can alter dMMR results.

## Fields

- Kind: Biomarker
- Last checked: 2026-09-23
- Also known as: dMMR; MMR-deficient; mismatch repair deficient; MMRd; loss of MLH1; loss of MSH2; loss of MSH6; loss of PMS2; MMR IHC; MMR protein loss
- Tags: biomarker; mmr

## Sources

- KEYTRUDA prescribing information (DailyMed): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9333c79b-d487-4538-a9f0-71b91a02b287
- Jemperli prescribing information (DailyMed): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=095eab9f-545a-4f12-bfb7-19477fb901a5

## Connected records

- biomarkers: [MSI-high (microsatellite instability by PCR or sequencing)](https://onco.cc/biomarkers/msi-high/), [TMB-high (tumour mutational burden >= 10 mutations per megabase)](https://onco.cc/biomarkers/tmb-high/), [TP53 mutation and del(17p)](https://onco.cc/biomarkers/tp53-del17p/)
- 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/), [Durvalumab](https://onco.cc/drugs/durvalumab/), [Ipilimumab](https://onco.cc/drugs/ipilimumab/), [Nivolumab](https://onco.cc/drugs/nivolumab/), [Pembrolizumab](https://onco.cc/drugs/pembrolizumab/), [VENTANA MMR RxDx Panel](https://onco.cc/drugs/ventana-mmr-rxdx/)
- terms: [Immunohistochemistry (IHC)](https://onco.cc/terms/ihc/), [Microsatellite instability (MSI-H) / mismatch repair deficiency (dMMR)](https://onco.cc/terms/msi/), [MLH1 promoter methylation (sporadic versus Lynch mismatch repair loss)](https://onco.cc/terms/mlh1-promoter-methylation/), [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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