# Microsatellite instability in Japanese female patients with triple-negative breast cancer

Source: https://onco.cc/key-papers/paper-kurata-japanese-tnbc-msi-breast-cancer-2020/  
OnCo record `paper-kurata-japanese-tnbc-msi-breast-cancer-2020` (Key paper). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Two of 228 Japanese triple-negative breast cancers, under 1%, were MSI-high; both were aggressive basal-like tumours without BRCA-like features.

## Summary

MSI in 228 TNBCs was evaluated with the Promega MSI Analysis System 1.2 (BAT-26, NR-21, BAT-25, MONO-27, NR-24) without normal tissue controls. 222 (97.4%) were stable, 4 (1.7%) MSI-low and 2 (0.9%) MSI-high; the two MSI-high tumours were nuclear grade 3, Ki-67 above 30%, basal-like and non-BRCA-like, with inconsistent TILs, CD8 and PD-L1.

## Fields

- Kind: Key paper
- Last checked: 2026-09-24
- Journal: Breast Cancer
- Year: 2020
- DOI: 10.1007/s12282-019-01043-5
- Authors: Kurata K, Kubo M, Kai M, et al.
- Findings: MSI-high 2 of 228 (0.9%); MSI-low 1.7%.; MSI-high tumours were grade 3, Ki-67-high and basal-like.
- What it means: Rare MSI-high TNBC exists and qualifies for tumour-agnostic pembrolizumab, so comprehensive genomic profiling should report MSI even though dedicated testing is low-yield.
- Caveats: No matched normal; small numbers of positives.; Japanese single-region cohort.

## Sources

- Kurata et al., Breast Cancer 2020: MSI in 228 Japanese TNBC patients: https://doi.org/10.1007/s12282-019-01043-5
- PubMed: https://pubmed.ncbi.nlm.nih.gov/31907878/

## Connected records

- biomarkers: [MSI-high (microsatellite instability by PCR or sequencing)](https://onco.cc/biomarkers/msi-high/)
- cancers: [Triple-negative breast cancer (TNBC)](https://onco.cc/cancers/tnbc/)
- targets: [Mismatch repair proteins (MLH1, MSH2, MSH6, PMS2)](https://onco.cc/targets/mmr/)
- terms: [Microsatellite instability (MSI-H) / mismatch repair deficiency (dMMR)](https://onco.cc/terms/msi/)
- journals: [Breast cancer](https://onco.cc/journals/breast-cancer-jbcs/)

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