A case of severe interstitial cystitis associated with pembrolizumab

Immune checkpoint inhibitors have emerged as a cornerstone of management in non-small-cell lung cancer (NSCLC). They are responsible for a wide spectrum of immune-related adverse effects, which greatly differ from the adverse events of standard chemotherapy. In this report, we describe a unique case of severe non-infectious cystitis in a patient receiving pembrolizumab for metastatic NSCLC. A 56-year-old female patient received first-line pembrolizumab for multimetastatic NSCLC, with a PD-L1 status of 90%. After 5 cycles, the patient presented with hematuria, urinary burning, urgent polyuria, painful urination and afebrile diarrhea. Urine was sterile, with a highly inflammatory cytology and high protein content. Diarrhea abated under symptomatic treatment but urinary symptoms persisted. Uroscanner found thickened, irregular bladder walls. Cystoscopy revealed a highly inflammatory and irregular mucosa, with diffuse inflammation and vasculo-exudative ulcerative remodeling on pathology. Grade 3 interstitial cystitis was diagnosed and attributed to immunotherapy. Following suspension of pembrolizumab and administration of systemic steroids, the patient had an excellent clinical and radiological response. Because of thoracic progression, oncological treatment was resumed with third-line paclitaxel-bevacizumab. Overall, this case highlights a novel toxicity of immune checkpoint inhibitors. Appropriate and timely diagnosis of rare immune-related adverse events is essential, as proper management of these toxicities may enable ICI continuation in patients who benefit the most from immunotherapy.