Pembrolizumab‐Induced Chronic Rhinosinusitis in a Patient With Non‐Small Cell Lung Cancer

A 63-year-old man was administered pembrolizumab for stage IV squamous cell lung cancer. After 54 cycles of pembrolizumab, the patient maintained complete remission of lung cancer but developed nasal obstruction, olfactory disturbance, conjunctivitis, stomatitis, glossitis, pharyngitis, and weight loss. Laboratory data showed increased levels of neutrophils, eosinophils, C-reactive protein, squamous cell carcinoma antigen, and cytokeratin 19 fragments. Sinus computed tomography revealed obstruction of the maxillary, ethmoid, and sphenoidal sinuses. Histological examination of nasal septal tissue revealed chronic rhinosinusitis with infiltration primarily of eosinophils, neutrophils, CD3⁺CD8⁺ T lymphocytes, and CD20⁺ B lymphocytes, along with destruction of nasal epithelium and glands. The patient was diagnosed with immune-related chronic rhinosinusitis and treated with oral prednisolone after discontinuation of pembrolizumab. Herein, we report a rare case of pembrolizumab-induced chronic rhinosinusitis without nasal polyps that was successfully treated with oral corticosteroid therapy.