Clinical significance of systemic immune-inflammation index (SII) and C-reactive protein-to-albumin ratio (CAR) in patients with esophageal cancer: a meta-analysis

Background: Numerous studies have reported that systemic immune-inflammation index (SII) and C-reactive protein-to-albumin ratio (CAR) correlate with tumor progression and prognosis in various types of human cancer. The aim of this study is to systematically investigate the clinical significance of SII and CAR in esophageal cancer (EC). Methods: We searched a number of databases for articles reporting the effect of pretreatment SII and CAR on the survival of EC patients. Review Manager 5.3 and STATA/SE 14.1 were applied in this meta-analysis. The multivariable-adjusted hazard ratio (HR) was used for calculating the relationship between SII and CAR and overall survival (OS), and the odds ratio (OR) was applied for the clinical pathology. Results: Five original studies for SII and seven original datasets for CAR were included for analysis. Increased SII showed a significant association with shorter OS in EC patients after surgery (HR: 1.34, 95% CI: 1.15–1.53, P<0.001) and high CAR indicated worse long-term OS in EC (HR: 1.60, 95% CI: 1.29–1.90, P<0.001). Different subgroup analyses were also confirmed the prognostic roles in EC patients. Furthermore, the adverse impacts of elevated SII and CAR on tumor progression were revealed in the infiltration depth, lymph node metastasis, and clinical stage. Conclusions: Both pretreatment SII and CAR might be promising predictors of cancer survival and tumor progression in EC. Further studies are warranted to verify the clinical usefulness in patients with EC.