Immunotherapy-Related Cystitis Induced by Nivolumab for Advanced Gastric Cancer: A Case Report.

A 70-year-old man received treatment for advanced gastric cancer involving capecitabine, oxaliplatin, and nivolumab therapy. Following four courses of this treatment, he developed severe urethralgia and hematopyuria. Urine bacterial culture was negative. Cystoscopy revealed readily bleeding and edematous, reddish mucosa. Computed tomography identified edematous changes in the wall of the bladder, but no lesions were noted in the upper urinary tract. The bladder wall was biopsied, and pathological findings indicated erosion and hemorrhage of the bladder mucosa, accompanied by lymphocytic infiltration. Based on the overall clinical presentation, immunotherapy-associated cystitis induced by nivolumab treatment for advanced gastric cancer was suspected. He began taking prednisolone at a dosage of 25 mg per day, which was gradually tapered over time, and the urinary symptoms markedly improved.