Relationship Between Systemic Immune-Inflammation Index and All-Cause Mortality in Stage IIIB–IV Epidermal Growth Factor Receptor - Mutated Lung Adenocarcinoma

Chi Zhang^1*Chao Yang²

• ¹Anhui Chest Hospital, Hefei, China
• ²Anhui Provincial Children's Hospital, Hefei, China

Background: This study seeks to investigate the relationship between the systemic immune-inflammation index (SII) and all-cause mortality (ACM) risk among individuals with Stage IIIB-IV epidermal growth factor receptor (EGFR)-mutated lung adenocarcinoma. Methods: The clinical data of 187 individuals with stage IIIB–IV EGFR-mutated lung adenocarcinoma from Anhui Chest Hospital from June 2017 to December 2023 were collected retrospectively for analysis. The SII was calculated as platelet count × neutrophil count/lymphocyte count. The receiver operating characteristic (ROC) curve was employed to evaluate the optimal threshold value for SII, and individuals were classified as low and high SII groups. ACM serves as the primary endpoint. Univariate and multivariate analyses were carried out via Cox proportional hazards models. The robustness of the findings was tested by subgroup and sensitivity analyses. Results: The ACM risk was notably elevated in the high SII group (P=0.001) in comparison to the low SII group. Multivariate Cox analysis demonstrated that SII can independently predict poor prognosis. In the fully adjusted model, in comparison with the low SII group, the ACM risk was 1.985 times higher in the high SII group (HR=1.985, 95% CI: 1.216–3.240, P=0.006). Subgroup analyses demonstrated that SII was more notably linked to ACM risk in men (HR=3.245, P=0.005) and such a relationship was also significant among female patients (HR=2.036, P=0.048). In individuals aged ≥65 years, a high SII was notably linked to an elevated ACM risk (HR=2.675, P=0.004). Nevertheless, no such relationship was found in individuals aged under 65. Sensitivity analyses suggested that high SII remained notably correlated with an elevated ACM risk after excluding individuals with special types of adenocarcinoma, stage III lung adenocarcinoma, or diabetes (all P<0.05), supporting its potential as an independent prognostic indicator. ROC curve analysis demonstrated that SII had a moderate predictive ability for ACM, with an AUC of 0.669 (95% CI: 0.527–0.812, P=0.021). Conclusion: Elevated SII is an independent biomarker for predicting ACM in individuals with Stage IIIB–IV EGFR-mutated lung adenocarcinoma with stronger predictive value in male and older populations.