Prognostic value of the systemic immune-inflammation index in recurrent/metastatic triple-negative breast cancer: a retrospective cohort study.

Background: Local relapse and distant metastasis are the primary causes of treatment failure and mortality in patients with breast cancer. Triple-negative breast cancer (TNBC) is characterized by limited treatment options, high rates of relapse and metastasis, and poor survival rates. This study aimed to explore the prognostic importance of the systemic immune-inflammation index (SII) among patients with recurrent/metastatic TNBC, focusing on the potential of SII as a novel biomarker for survival prediction. Methods: This retrospective research involved 62 patients with recurrent/metastatic TNBC who received secondary surgery in Peking Union Medical College Hospital following primary surgery between 2005 and 2018. Clinical data on the preoperative SII, tumor characteristics, and survival outcomes were collected. Receiver operating characteristic (ROC) curve analysis was used for determining the SII optimum cutoff value of 460.45, which was utilized to divide patients into high SII (≥460.45) and low SII (<460.45) groups. Cox regression models, as well as Kaplan-Meier survival curves, were used to evaluate post-recurrence survival (PRS). Results: In the high SII group, the patients' PRS was significantly shorter than that of patients in the low SII group (log-rank P=0.007). Multivariate Cox regression analysis identified a tumor size of >5 cm and a high preoperative SII as independent risk factors for poor prognosis. Notably, 69.4% of the recurrent/metastatic lesions retained the TNBC subtype, whereas 30.6% had molecular subtype changes. Distant metastasis was correlated with worse PRS (log-rank P=0.001); however, changes in tumor molecular subtype did not significantly affect PRS. Conclusions: The SII is a cost-effective prognostic biomarker for recurrent/metastatic TNBC, reflecting systemic inflammation and immune dysregulation. The dynamic interactions between tumor microenvironment (TME) and systemic inflammation underscore the clinical application of the SII in patient risk stratification and therapeutic decision making. These findings advocate for the integration of SII into routine prognostic assessments and emphasize the importance of repeat biopsy in guiding personalized treatment strategies for patients with recurrent/metastatic TNBC.