Onset and Outcomes of Immune-related Adverse Events in Genitourinary Cancer Treated With Immune Checkpoint Inhibitors

Background/Aim: Immune checkpoint inhibitors are widely used in treating metastatic urothelial carcinoma and metastatic renal cell carcinoma. However, the incidence, timing, and clinical impact of immune-related adverse events in real-world practice remain unclear. This study aimed to investigate their onset patterns and outcomes. Patients and Methods: We retrospectively analyzed 210 patients with metastatic urothelial carcinoma (n=127) or metastatic renal cell carcinoma (n=83) treated with immune checkpoint inhibitors between 2017 and 2023 at a single academic institution. Events were graded using Common Terminology Criteria for Adverse Events version 5.0. Associations with progression-free and overall survival were assessed. We also evaluated cumulative incidence, corticosteroid or immunosuppressant use, and outcomes after rechallenge. Results: Immune-related adverse events occurred in 78 patients (37.1%), more frequently in metastatic renal cell carcinoma (47.0%) than in metastatic urothelial carcinoma (30.9%). Overall, grade ≥3 events occurred in 22.0% of patients, with higher incidence in renal cell carcinoma (27.7%) than in urothelial carcinoma (17.3%). In metastatic urothelial carcinoma, their presence was linked to longer survival; no difference was seen in metastatic renal cell carcinoma. Most events developed within six months; only 3.4% occurred after one year. High-dose corticosteroids were administered in 13.8% of patients, and 72.4% of them successfully completed tapering. Immunosuppressants were used in 1.4%. Eleven patients underwent rechallenge, of whom two experienced recurrence. Conclusion: Immune-related adverse events showed distinct incidence and prognostic relevance between urothelial and renal cell carcinoma. These findings underscore the need for treatment-specific monitoring and provide practical insights into managing toxicities and decisions regarding immunotherapy rechallenge.