Prognostic value of the systemic immune-inflammation index in patients with breast cancer: a meta-analysis

Background Although previous studies have evaluated the prognostic role of the systemic immune-inflammation index (SII) in patients with breast cancer, the results were inconsistent. Therefore, in this context, we aimed to identify the prognostic and clinicopathological value of the SII in patients with breast cancer by performing a meta-analysis. Methods A literature search was using PubMed, Web of Science, EMBASE, and Cochrane Library databases for relevant articles, from their inception to May 12, 2020. The prognostic value of the SII in breast cancer was assessed by pooling the hazard ratios (HRs) with 95% confidence intervals (CIs). The clinical outcomes included the overall survival (OS), disease-free survival (DFS), recurrence-free survival (RFS), and distant metastasis-free survival (DMFS). The methodological quality of all the included studies was evaluated using the Newcastle-Ottawa quality assessment scale. The odds ratios (ORs) with 95% CIs were combined to evaluate the correlation between the SII and clinicopathological characteristics of patients with breast cancer. Publication bias was evaluated using the Begg funnel plot and the Egger linear regression test. All statistical analyses were performed using Stata software, version 12.0 (Stata Corporation, College Station, TX, USA). Apvalue of < 0.05 was considered statistically significant. Results Eight studies involving 2642 patients were included in the current meta-analysis. The combined data showed that patients with a high SII had worse OS (HR = 1.79, 95% CI 1.33-2.42, p < 0.001), poorer DFS/RFS (HR = 1.79, 95% CI 1.31-2.46, p < 0.001), and inferior DMFS (HR = 1.64, 95% CI 1.32-2.03, p < 0.001) than patients with a low SII. In addition, a high SII was correlated with the presence of lymph node metastasis (OR = 1.38, 95% CI 1.12-1.69, p = 0.002), higher T stage (OR = 1.49, 95% CI 1.17-1.89, p < 0.001), advanced TNM stage (OR = 1.37, 95% CI 1.07-1.77, p = 0.014), and higher histological grade (OR = 3.71, 95% CI 1.00-13.73, p = 0.049). However, there was no significant association between the SII and the pathological type (OR = 0.82, 95% CI 0.55-1.23, p = 0.345) or lymphatic invasion (OR = 1.30, 95% CI 0.82-2.08, p = 0.266). Conclusions The results of our meta-analysis suggest that an elevated SII predicts poor survival outcomes and is associated with clinicopathological features that indicate tumor progression of breast cancer.