High systemic immune-inflammation index predicts poor prognosis and response to intravesical BCG treatment in patients with urothelial carcinoma: a systematic review and meta-analysis

Background The systemic immune-inflammation index (SII) has emerged as a promising marker predicting the prognosis of some cancers, while its role in urothelial carcinoma (UC) remains uncertain, especially in upper urinary tract urothelial carcinoma (UTUC). This meta-analysis aimed to investigate the association of SII with the prognosis of UC and the response to intravesical Bacillus Calmette-Guerin (BCG) therapy of non-muscle invasive bladder cancer (NMIBC).Methods A systematic search in PubMed, Embase, Web of Science, and the Cochrane Library was performed to identify relevant studies. The extracted hazard ratios (HRs) and 95% confidence intervals (CIs) were used to evaluate the association between SII and overall survival (OS), cancer-specific survival (CSS), and recurrence-free survival (RFS) of patients with UC. Additionally, we pooled odds ratios (ORs) and 95% CIs to assess the relationship between SII and BCG response in patients with NMIBC. Subgroup and sensitivity analyses were performed to explore potential sources of heterogeneity.Results Twenty studies comprising a total of 12,645 patients were eligible. This meta-analysis revealed that high SII levels independently increased the risk of OS (HR 1.55, 95%CI 1.25-1.92), CSS (HR 1.82, 95%CI 1.36-2.45), and RFS (HR 1.26, 95% CI 1.18-1.35) in patients with UC, including those with upper tract urothelial carcinoma. Additionally, elevated SII levels could predict a lower response to intravesical BCG treatment (OR 0.18, 95%CI 0.07-0.45) and higher disease recurrence (HR 1.61, 95%CI 1.31-1.98) in patients with NMIBC. Furthermore, elevated SII levels were positively associated with advanced age, lymphovascular invasion, hydronephrosis, and high tumor grade and stage (pT >= 3).Conclusions Elevated preoperative SII levels are associated with poor survival outcomes in patients with UC, as well as worse response to BCG treatment in patients with NMIBC. Therefore, SII can serve not only as an independent prognostic predictor of patients with UC but also as a guide for BCG therapy in NMIBC.Systematic review registration https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42023409077, identifier CRD42023409077.