Prognostic value of preoperative systemic immune-inflammation index in patients with bladder cancer undergoing radical cystectomy: a systematic review and meta-analysis.

Background: To improve risk stratification in patients with bladder cancer (BC) undergoing radical cystectomy (RC), the systemic immune-inflammation index (SII), calculated from routine blood parameters, has attracted attention as a promising prognostic biomarker. This meta-analysis aims to synthesize existing evidence regarding the prognostic utility of SII and to elucidate its potential clinical significance. Methods: This systematic review and meta-analysis, conducted in accordance with the PRISMA framework, included nine cohort studies with a combined total of 6,288 participants. The prognostic impact of preoperative SII on postoperative outcomes was assessed by calculating pooled hazard ratios (HRs) using a random-effects model. Publication bias was assessed using funnel plots, Begg's test, and Egger's test, and its potential impact on the pooled estimates was critically evaluated. Results: The analysis revealed a significant correlation between elevated preoperative SII and adverse oncological outcomes. Notably, a higher SII was significantly associated with reduced overall survival (OS) (HR = 1.35, 95% CI: 1.15-1.59; p < 0.001). For recurrence-free survival (RFS), a potential association was observed (HR = 1.20, 95% CI: 1.01-1.41; p = 0.03); however, this finding was not robust in leave-one-out sensitivity analysis and should be considered highly tentative. For cancer-specific survival (CSS), a trend toward worse outcomes was noted (HR = 1.34, p = 0.05), suggesting a potential link that merits further investigation, however, this result was based on only three studies and should be interpreted with caution. Conclusions: The present study reveals that a high preoperative SII is associated with poorer OS in patients with BC undergoing RC, supporting its promise as a useful prognostic marker. However, these findings were markedly limited by substantial heterogeneity and clear evidence of publication bias (particularly for OS and RFS), suggesting that the true effect size may be smaller than estimated. To translate this promising finding into clinical practice, future large-scale, prospective multicenter studies are warranted. Such studies should focus on using standardized SII cut-offs and methodologies to validate its prognostic accuracy and suggest SII as a candidate prognostic marker worthy of further investigation. However, current evidence is insufficient to support its routine clinical use, particularly for RFS and CSS. Systematic review registration: https://www.crd.york.ac.uk/PROSPERO/, identifier CRD420251057070.