What happened, in summary

This 77-year-old man had postoperative recurrent metastatic squamous cell lung cancer. He had received carboplatin, pemetrexed, and pembrolizumab for about 2 years, but anticancer therapy was stopped because the tumor grew. Radiation therapy was not used for the lung cancer. About 6 months after pembrolizumab was discontinued, he developed anorexia and vomiting and was admitted for evaluation. Examination found epigastric tenderness. CT showed marked thickening of the stomach wall from the fundus to the body, and upper endoscopy showed diffuse redness, edema, white exudate, easy bleeding, and very fragile gastric mucosa. He was diagnosed first with hemorrhagic gastritis and treated with fasting and proton pump inhibitors, but symptoms and endoscopic findings did not improve after 1 week. Biopsy from the gastric body showed inflammatory infiltration mainly by neutrophils and lymphocytes, with CD8-positive lymphocytes on immunostaining. There was no malignant epithelial change, amyloid, cytomegalovirus inclusion, or Helicobacter pylori infection. Considering the CT, endoscopy, biopsy, and history of immune checkpoint inhibitor treatment, his team diagnosed severe immune-related gastritis. Oral prednisolone 0.5 mg/kg was started, then increased to IV prednisolone 1.0 mg/kg when symptoms and endoscopic findings remained poor. Because the gastritis was steroid-refractory, infliximab 5 mg/kg was added. CT after the first infliximab dose showed marked improvement in gastric wall thickening, and vomiting and anorexia gradually improved. He received 3 infliximab doses while steroids were tapered. Three months after steroid treatment began, endoscopy and biopsy showed major improvement. The cancer status remained concerning because tumor growth had already stopped anticancer treatment, but the severe immune-related stomach inflammation responded once immunosuppression was escalated beyond steroids.