Non-bacterial cystitis with increased expression of programmed death-ligand 1 in the urothelium: An unusual immune-related adverse event during treatment with pembrolizumab for lung adenocarcinoma.

INTRODUCTION:Immune checkpoint inhibitors are now a standard therapeutic option for lung adenocarcinoma. However, Immune checkpoint inhibitors often induce various immune-related adverse events. CASE PRESENTATION:The patient was a 78-year-old woman with lung adenocarcinoma who had a partial response to pembrolizumab. During treatment, she complained of pollakiuria and nocturia with painful micturition. Histological analysis revealed infiltration of CD8-positive and/or TIA-1 cytotoxic granule-associated RNA binding protein-positive lymphocytes and programmed death-ligand 1 expression in the urothelium. A diagnosis of immune-related adverse event cystitis was made based on these clinical and pathological findings. The patient's subjective symptoms and findings on cystoscopy improved dramatically after treatment with prednisolone. CONCLUSION:Immune checkpoint inhibitors-induced cystitis is extremely rare. This report is the first to include an immunohistochemical analysis of the urothelial epithelium in immune-related adverse event cystitis and describes an instructive case.