Association Between Immune-Related Adverse Events and Efficacy and Changes in the Relative Eosinophil Count Among Patients with Advanced Urothelial Carcinoma Treated by Pembrolizumab

BACKGROUND: To evaluate the association between immune-related adverse events (irAEs) and the clinical outcomes and also between irAEs and the post-treatment changes in the relative eosinophil count (REC) in advanced urothelial carcinoma (UC) patients treated with pembrolizumab. MATERIALS AND METHODS: This retrospective study analyzed 105 advanced UC patients treated with pembrolizumab after disease progression on platinum-based chemotherapy between January 2018 and June 2021. The association between the occurrence of irAEs and the efficacy of pembrolizumab was investigated. The change in the REC from before the initiation of pembrolizumab therapy, to three weeks after treatment and the incidence of irAEs were determined. RESULTS: Overall irAEs were associated with a significantly higher objective response rate (ORR) (58.8% vs 25.4%, P<0.001), a longer progression-free survival (PFS) (25.1 months vs 3.1 months, P< 0.001) and overall survival (OS) (31.2 months vs 11.5 months, P< 0.001) compared to patients without irAEs; however, grade ≥3 irAEs were not associated with the ORR (36.4% vs 36.2%, P=0.989), PFS (9.5 vs 5.5 months, P=0.249), or OS (not reached vs 13.7 months, P=0.335). Compared to a decreased REC at 3 weeks after pembrolizumab, an increased relative REC at 3 weeks was not associated with the incidence of any-grade irAEs (32.3% vs 32.5%, P=0.984) or of grade ≥3 irAEs (10.8% vs 10.0%, P=0.900). Multivariate analyses revealed a female sex (P=0.005), Eastern Cooperative Oncology Group Performance Status ≥1 (P=0.024), albumin <3.7 g/dl (P<0.001), decreased REC (3 weeks later) (P<0.001), and the absence of irAEs of any grade (P=0.002) to be independently associated with a worse OS. CONCLUSION: Patients with irAEs showed a significantly better survival compared to patients without irAEs in advanced UC treated with pembrolizumab. An increased posttreatment REC may be a marker predicting improved clinical outcomes and it had no significant relationship with the incidence of irAEs.