Clinicopathological and prognostic importance of systemic immune inflammation index (SII) in breast cancer patients: a meta-analysis

Background: The relationship between systemic immune inflammation index (SII) and prognosis of malignancies is an original research topic that has intrigued great interests. However, the clinicopathological significance and prognostic value of it in breast cancer are still disputed. To solve this issue, a meta-analysis was performed on breast cancer patients. Methods: Suitable and relevant studies in PubMed, EMBASE, Web of Science, Cochrane Library, China National Knowledge Infrastructure (CNKI), and SinoMed, were systematically retrieved. The endpoints set included disease-free survival (DFS), overall survival (OS), and clinicopathological features. Additionally, the hazard ratio (HR) and 95% confidence interval (CI) were incorporated into analyzing the correlation of pretreatment SII with OS and DFS in breast cancer patients, while the clinicopathological features were characterized by the odds ratio (OR). Results: 1,768 patients from eight studies were included. The results indicated that poor OS (pooled HR: 1.82, 95% CI: 1.28-2.59, P=0.0009) and DFS (pooled HR: 1.79, 95% CI: 1.26-2.54, P=0.001) had a considerable correlation with increased SII, and the role of SII in prognosis was further confirmed by subgroup analysis. Additionally, elevated pretreatment SII was also associated with T stage (T2-4), menstrual status (pre-menstrual), and ER status (ER+). Conclusions: A predictive biomarker for elevated pretreatment SII in worse survival of patients with breast cancer was suggested.