In recent years, great successes have been achieved with immunotherapy in various tumor entities. However, the response to immunotherapy can be delayed, and this can sometimes be a major challenge for those treating the disease, as the distinction between progressive disease and pseudoprogression is difficult and the optimal time for a definitive response is not well defined.

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A case of a patient with gastric cancer (GC) who was treated with immunotherapy after relapse and showed continuous improvement, but eventually a significant response without changing treatment.

Gastric adenocarcinoma accounts for 95% of gastric malignancies and is the most common malignancy and the fourth leading cause of death. Although surgical removal of the tumor is curative, especially in the early stages, most affected individuals still experience disease recurrence. Immunotherapy combined with antiangiogenic therapy has significantly improved prognosis. Tumors with high microsatellite instability (MSI-H) are more susceptible to treatment with immune checkpoint inhibitors.
The present case involves a 59-year-old man diagnosed with gastric adenocarcinoma (pT1N0M0, stage IA) based on gastroscopic biopsy. After proximal subtotal gastrectomy, no further treatments were performed and the patient remained in good general condition.