Colonic Metastases from Lung Adenocarcinoma Detected During an Evaluation of Recurrent Diarrhea Associated with Immune-Related Colitis.

A 74-year-old man with advanced lung adenocarcinoma developed grade 3 diarrhea after treatment with pembrolizumab. Colonoscopy and a biopsy initially suggested immune-related adverse event colitis (irAE colitis), and the symptoms improved with corticosteroid therapy. However, grade 3 diarrhea recurred during prednisolone tapering, raising a suspicion of recurrent colitis. Radiological progression of the associated intra-abdominal lymphadenopathy was also observed. Repeat colonoscopy before infliximab administration revealed multiple colonic metastases from lung adenocarcinoma. Gastrointestinal metastases should be considered in patients with atypical clinical or radiological findings, and repeated endoscopic evaluations may be useful before escalating immunosuppressive therapy.