[A Case of Advanced Gastric Cancer of an Elderly Patient Responding Effectively to Pembrolizumab].

A 96-year-old man was admitted to our hospital because of dysphagia. After examination, he was diagnosed with type 3 advanced gastric cancer in the antrum with duodenal invasion. A gastrojejunostomy was performed because of dissemination in the pelvic floor. He was put on pembrolizumab after surgery because the microsatellite instability test showed positive results. The therapeutic response was PR. Pembrolizumab can improve the outcomes in elderly patients with unresectable advanced gastric cancer.