Systemic Immune-Inflammation Index as a Prognostic Marker in Gastric and Gastroesophageal Junction Cancers Receiving Perioperative FLOT Therapy

Background and Objectives: The systemic immune-inflammation index (SII), derived from peripheral blood parameters, has emerged as a novel marker reflecting the balance between host immunity and tumor-related inflammatory burden. This study aimed to investigate the prognostic impact of baseline SII on survival outcomes in patients with gastric or gastroesophageal junction (GEJ) cancer undergoing perioperative FLOT (5-fluorouracil, leucovorin, oxaliplatin, and docetaxel) chemotherapy. Materials and Methods: In this retrospective study, 168 patients with histologically confirmed gastric or GEJ cancer who received perioperative FLOT therapy were included. SII was calculated using the formula: SII = (Platelets × Neutrophils)/Lymphocytes. ROC curve analysis determined the optimal SII cutoff for predicting mortality. Patients were categorized into low (SII ≤685) and high (SII >685) groups. Overall survival (OS) and disease-free survival (DFS) were evaluated using Kaplan–Meier analysis and compared via the log-rank test. Cox proportional hazards regression models were used for univariate and multivariate analysis. Results: The optimal cutoff value for SII was determined to be 685 (AUC: 0.652, 95% CI: 0.558–0.747, p = 0.003). High SII was significantly shorter OS (17.4 vs. 28.2 months, p = 0.001) Multivariate analysis identified high SII (HR = 1.88, 95% CI: 1.36–2.89, p = 0.039), advanced T stage (HR = 3.693, p < 0.001), poor treatment response (HR = 0.36, p < 0.001), and ECOG-PS ≥1 (HR = 3.297, p < 0.001) as independent predictors of mortality. Conclusions: Elevated baseline SII is an independent predictor of worse OS and DFS in gastric and GEJ cancer patients receiving perioperative FLOT chemotherapy. SII may serve as a practical and inexpensive biomarker to support risk stratification and personalized treatment decisions.