Pseudoprogression presenting as intestinal perforation in non-small cell lung cancer treated with anti-PD-1: A case report.

Pseudoprogression is not frequently observed in patients with non-small cell lung cancer (NSCLC) who are treated with immune checkpoint inhibitors. We report on a case of pseudoprogression, which was presented as intestinal perforation after pembrolizumab immunotherapy for NSCLC. A-54-year-old man with stage IV NSCLC received pembrolizumab therapy. The patient was admitted to our hospital because of acute abdominal pain and the computed tomography scan revealed diffuse wall thickening of the small bowel with free intraperitoneal air. Intestinal perforation was suspected and surgical resection was performed. Histological evaluation of the resected specimen showed infiltrated lymphocytes positive for CD3, CD8 with necrotic tumor cells, suggestive of an immune reaction. Although intestinal perforation after treatment with immune checkpoint inhibitors is rare, it can be an unusual presentation of pseudoprogression and clinicians should be aware of this possibility.