MSI-H vs pMMR: what does it mean for treatment?

MSI-H/dMMR tumors: high neoantigen load, brisk TIL, excellent IO response. pMMR/MSS: cold tumors with poor IO response. KEYNOTE-158 showed 36% ORR for MSI-H solid tumors across 10 tumor types.

What percentage of CRCs are MSI-H?

Approximately 15% of stage I–III CRC and 4–5% of metastatic CRC is MSI-H. Stage II MSI-H: better prognosis without chemotherapy (5-FU may be detrimental). Stage IV MSI-H: IO eligible.

PCR-based MSI testing (gold standard), IHC for MMR proteins (MLH1, MSH2, MSH6, PMS2), or NGS-based MSI scoring. IHC loss of MLH1 with concurrent MLH1 promoter methylation indicates sporadic MSI-H (not Lynch syndrome).

MSI-H Immunotherapy Response Probability Calculator

Estimate immunotherapy response probability in MSI-H/dMMR colorectal cancer. Pembrolizumab first-line: ORR 45%, PFS2 advantage vs chemotherapy. MMR status guides checkpoint inhibitor eligibility.

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Frequently Asked Questions

MSI-H vs pMMR: what does it mean for treatment?

What percentage of CRCs are MSI-H?

How is MSI-H tested?