Occult diffuse jejunal metastasis from poorly differentiated non-small cell lung cancer mimicking immune checkpoint...

Gastrointestinal metastases from non-small cell lung cancer (NSCLC) are rare and usually focal. Diffuse small bowel involvement without discrete lesions is uncommon and often radiographically occult.An elderly man with a history of poorly differentiated NSCLC, previously treated with pembrolizumab, presented with recurrent ascites, profound anasarca, dizziness and anaemia. Multiple endoscopic evaluations, CT scans and a positron emission tomography-CT were unrevealing. Due to prior immunotherapy exposure and diffuse jejunal inflammation, immune checkpoint inhibitor enteritis was suspected, showing transient response to corticosteroids. However, push enteroscopy later revealed diffuse, friable proximal jejunal mucosa. Biopsy confirmed metastatic carcinoma (cytokeratin 7 positive, cytokeratin 20, caudal-type homeobox transcription factor 2 and thyroid transcription factor 1 negative), and molecular profiling showed 80% programmed death-ligand 1 expression. The patient's condition deteriorated and he died shortly after the diagnosis was made.This case emphasises that diffuse intestinal metastases can evade conventional imaging and superficial biopsies, mimicking immunotherapy-related enteritis. Persistent clinical suspicion, repeat endoscopy and deep histopathological confirmation are vital.