Abstract
INTRODUCTION: Although immune checkpoint inhibitors offer significant therapeutic benefits to patients with advanced cancer, they can also cause a variety of immune-related adverse events. As immune checkpoint inhibitors are being widely used, rare immune-related adverse events are being reported. CASE PRESENTATION: A 70-year-old man with advanced salivary duct carcinoma was treated with pembrolizumab following radiotherapy. After receiving two doses of pembrolizumab, the patient experienced symptoms such as micturition pain and hematuria. Immune-related cystitis was suspected, and the patient underwent a bladder biopsy and bladder hydrodistension. Histological analysis revealed non-neoplastic bladder mucosa with CD8-positive lymphocyte-dominant inflammatory cell infiltration, consistent with immune-related cystitis. The patient's bladder symptoms improved postoperatively without steroid administration. CONCLUSION: Although steroids are commonly administered to treat immune-related adverse events, bladder hydrodistension may be a promising treatment option for immune-related cystitis to avoid administration of steroids, which may impair the therapeutic effect of immune checkpoint inhibitors.