Incorporation of Immunotherapy in MSI-H Gastric Cancer Treatment

Introduction to MSI-H Gastric Cancer Treatment

The National Comprehensive Cancer Network (NCCN) recommends nivolumab plus fluoropyrimidine and oxaliplatin-based chemotherapy as first-line treatment for MSI-H gastric cancer, independent of PD-L1 expression, with a Category 2A preferred option rating 1, 2, 3
MSI-H tumors demonstrate exceptional responses to checkpoint inhibitors regardless of PD-L1 status, with the NCCN 2025 guidelines supporting nivolumab plus chemotherapy as a preferred option 1, 2, 3

The survival benefit in MSI-H patients is dramatic, with a median OS of 38.7 months versus 12.3 months with chemotherapy alone (HR 0.34) in the CheckMate-649 trial subset analysis 1, 2, 3
For MSI-H patients with PD-L1 CPS ≥5, the benefit was even more pronounced: 44.8 months versus 8.8 months (HR 0.29) 1, 2, 3

Nivolumab 360 mg IV every 3 weeks (or 240 mg every 2 weeks) plus FOLFOX or CAPOX is a Category 2A preferred option for MSI-H tumors regardless of PD-L1 status 1, 2, 3, 5
Continue nivolumab for up to 24 months or until disease progression or unacceptable toxicity 2, 3
The fluoropyrimidine-oxaliplatin backbone is preferred over cisplatin due to lower toxicity 5

Pembrolizumab monotherapy is a Category 2A preferred option for MSI-H tumors, with an ORR of 45.8% and median PFS of 11 months in previously treated MSI-H gastric cancer 6, 7
Nivolumab plus ipilimumab is a Category 2A preferred option for first-line MSI-H disease, with a median OS not reached versus 10 months with chemotherapy (HR 0.28) in the CheckMate-649 trial 1, 2, 3

Grade 3-4 treatment-related adverse events occurred in 59% with nivolumab plus chemotherapy versus 44% with chemotherapy alone in CheckMate-649 2, 3
Sixteen treatment-related deaths occurred in the nivolumab plus chemotherapy group versus 4 in chemotherapy alone 2, 3
Monitor closely for immune-related adverse events including colitis, hepatitis, pneumonitis, and endocrinopathies 2, 3

Restage after 2-3 cycles with CT imaging to assess response 1
Consider surgical resection if downstaging occurs and the patient becomes resectable with clear margins achievable 1
Continue immunotherapy for up to 24 months if good response and tolerability 2, 3