Abstract
Introduction: Breast carcinoma is the most common neoplasm among women. On the other hand, many inflammation markers are correlated with carcinoma prognosis. Our investigation sought to evaluate how the systemic immune‑inflammation (SSI) index is associated with the likelihood of developing breast cancer.
Materials and Methods: Web of Science, Cochrane, Scopus, PubMed, Embase, and Google Scholar were searched for publications up to November 8, 2025, and the data were analyzed using STATA 14.
Results: In total, five observational studies with a sum of 520783 female participants were combined. Results of the studies demonstrated that high SII index levels strengthened the risk of breast neoplasm (OR: 1.09, 95% CI: 1.05, 1.13). The tertile 2 of the SII index was not associated with increased risk of breast neoplasm. However, the tertile 3 (9%), the quartile 2 (6%), the quartile 3 (6%), and the quartile 4 (32%) of the SII index increased the risk of breast neoplasm. Furthermore, high SII index levels among the women in the UK and the USA increased the probability of breast cancer by 7% and 18%, respectively, and in cohort and cross-sectional studies by 8% and 22%, respectively. Besides, female patients with diabetes mellitus who had high SII index levels faced a 3% higher risk of breast neoplasm than nondiabetic women.
Conclusion: A high SII index was a risk factor for the occurrence of breast neoplasm, and higher SII index levels in women were associated with higher risks of breast carcinoma. Additionally, women with high SII index levels who lived in the USA faced twice the risk of breast cancer compared with those who lived in the UK.
Registration: This study has been compiled based on the PRISMA checklist, and its protocol was registered on the PROSPERO (ID: CRD420251237998) and Research Registry (UIN: reviewregistry2062) websites.