What happened, in summary

A 75-year-old man was evaluated for persistent anemia, weight loss, and poor appetite. Imaging found a large gastric mass invading nearby tissues, with regional lymph-node involvement but no distant metastases. Biopsy showed poorly differentiated gastric adenocarcinoma with squamous differentiation. The tumor had very high PD-L1 expression, with a combined positive score of 75, and the cancer was classified as Stage IV.

Because surgery carried substantial risk, treatment began with modified FOLFOX6 chemotherapy plus nivolumab. He received 12 cycles. Imaging after several months showed a major partial response, and by June 2025 PET imaging showed no residual or recurrent disease, consistent with a complete radiologic and metabolic response.

He then moved to maintenance nivolumab plus oral capecitabine. During maintenance therapy he developed severe gastroenteritis and acute kidney injury, so both drugs were temporarily stopped while he received supportive treatment. Kidney function improved but did not return to its previous baseline. Nivolumab was later continued alone. By the most recent follow-up in March 2026, he remained clinically well with no evidence of cancer recurrence and had not required gastric surgery.