Systemic Immune-Inflammation Index and Prognostic Outcome of Breast Cancer: An Updated Systematic Review and Meta-Analysis

This current study sought to determine the prognostic ability of systemic immune-inflammation index (SII) in breast cancer (BC) patients.The predictive role of SII in pathologic complete response (pCR), of BC patients following neoadjuvant chemotherapy (NAC) was also investigated.This study adhered to the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines.A systematic search was conducted in the Medline, ProQuest, Google Scholar, ScienceDirect, and the Cochrane Library databases, using search terms related to BC (population), high SII (exposure), low SII (control), and prognostic (outcome) to identify and update the systematic review and meta-analyses.Studies evaluating the prognostic outcomes of SII in BC were included.The prognostic outcomes included overall survival (OS), disease-free survival (DFS), distant metastasis-free survival (DMFS) and pCR.Review Manager 5.4 was used to perform meta-analysis.A total of 28 studies were included.Our study showed that a high SII was associated with worse OS [hazard ratio (HR)=1.88,95% confidence interval (CI): 1.51-2.33,p-value<0.00001;I 2 =68%], DFS (HR=2.10,95% CI: 1.60-2.75,p-value<0.00001;I 2 =77%), and DMFS (HR=1.89,95% CI: 1.37-2.59,p-value<0.0001,I 2 =49%) in BC patients.Notably, SII was unlikely to predict pCR in BC patients following NAC (HR=0.90, 95% CI: 0.69-1.18,p-value=0.46,I 2 =71%).This updated systematic review and meta-analysis demonstrated that an elevated SII may be a potential predictor of poor OS, DFS, and DMFS in BC patients, but not a predictor of positive pCR.However, the findings are limited by different cut-off values, significant heterogeneity, and the observational nature of the included data.