Pembrolizumab-Induced Acalculous Cholecystitis Mimicking Gallbladder Carcinoma on 18 F-FDG PET/CT

Lung cancer is one of the most common causes of cancer-related deaths. Immune checkpoint inhibitors (ICIs) have improved the survival of patients with metastatic lung cancer. But, by activating the immune system, they can lead to immune-mediated adverse events. Here we report a case of metastatic lung adenocarcinoma presenting with right upper abdominal pain after initiation of pembrolizumab. 18 F-FDG PET/CT highlighted the FDG avid thickening in the ICI-induced acalculous cholecystitis mimicking carcinoma gall bladder, which was confirmed on FNAC from the thickening and follow-up PET/CT imaging.