Purpose: Microsatellite instability-high (MSI-H) advanced gastric or esophagogastric junction cancer (AGC), accounting for 5%-6% of all AGC cases, has shown an enhanced responsiveness to immunotherapy. We performed a single-arm phase II study to evaluate the combination of nivolumab (NIVO) and low-dose (LD) ipilimumab (IPI) for first-line treatment of MSI-H AGC.
Patients and methods: Patients with MSI-H AGC received NIVO (240 mg once every 2 weeks) and IPI (1 mg/kg once every 6 weeks). The primary end point was overall response rate (ORR) assessed by blinded independent central review. Secondary end points included disease control rate (DCR), progression-free survival (PFS), overall survival (OS), safety, and biomarker analysis. MSI-H status was confirmed with an MSI-IVD Kit (Falco).
Results: Twenty-nine patients were enrolled. The ORR was 62.1% (95% CI, 42.3 to 79.3), with a complete response rate of 10.3%. The DCR was 79.3% (95% CI, 60.3 to 92.0). Treatment-related adverse events (TRAEs) of any grade occurred in 93.1% of patients, with those of grade ≥3 manifesting in 37.9% of patients. At the data cutoff (median follow-up of 9.0 months), treatment had been discontinued in 21 patients, with such discontinuation being due to TRAEs in 12 (41.4%) patients. However, after exclusion of one patient with progressive disease, the remaining 11 patients showed long-term antitumor efficacy after treatment discontinuation (range of response duration, 0.9+ to 15.6+ months). The median PFS was 13.8 months (95% CI, 13.7 months to not reached [NR]) and the median OS was NR (95% CI, 13.7 months to NR), with a 12-month OS rate of 79.5%.
Conclusion: NIVO plus LD-IPI showed robust and durable antitumor efficacy as a first-line treatment for MSI-H AGC. Although TRAEs often led to treatment discontinuation, treatment efficacy was subsequently sustained in most patients.