Systemic immune-inflammation index as a survival predictor in advanced urothelial carcinoma treated with avelumab maintenance.

e16559 Background: Systemic immune-inflammation index (SII) is a predictor of survival in patients with various malignancies. This analysis was performed to evaluate its prognostic value in advanced urothelial carcinoma (UC) receiving conventional chemotherapy followed by avelumab maintenance. Methods: Between December 2020 and December 2024, we enrolled 77 patients (54 males), median age 68 years, treated with platinum derivate + gemcitabine, median cycles 4, and following avelumab 800 mg biweekly. At chemotherapy initiation, SII was calculated as a platelet count × neutrophil-lymphocyte count ratio. Study population was divided based on median SII into high (≥ 758) and low (< 758). Progression-free survival (PFS) and overall survival (OS) were estimated by the Kaplan-Meier method with differences analyzed by the log-rank test. Multivariate Cox proportional-hazards model was performed to evaluate the prognostic value of performance status by the Eastern Cooperative Oncology Group (ECOG), metastatic status, and SII. Results: At the median follow up 18.1 months, 38 patients progressed on avelumab and 31 died. ECOG 2 was associated with significantly worse PFS and OS than ECOG 0 and 1 (HR 0.42; P = 0.0304 and HR 0.33; P = 0.0103, respectively). Both survivals were shorter in individuals with distant metastases compared to locally advanced disease or metastases only in the distant lymph nodes (HR 0.24; P = 0.0028 for PFS and HR 0.24; P = 0.0092 for OS). High SII was associated with worse PFS (HR 0.49; P = 0.0292) and OS (HR 0.43; P = 0.0225). The independent prognostic value of SII was shown in multivariate analyses. Conclusions: SII determined at chemotherapy initiation was an independent prognostic factor for both PFS and OS. Once validated, SII could be used to predict survival in patients with advanced UC treated with avelumab maintenance. Key Words: Systemic immune-inflammation index. Advanced urothelial carcinoma. Avelumab. Progression-free survival. Overall survival. Acknowledgements: OncoReSearch, Rovinka, Slovakia.