Preoperative Systemic Inflammatory Indices and Their Association with Tumor Burden and Surgical Outcomes in High-Grade Serous Ovarian Cancer

Background/Objectives: High-grade serous ovarian cancer (HGSOC) represents the most aggressive subtype of epithelial ovarian cancer and is frequently diagnosed at advanced stages. Increasing evidence suggests that systemic inflammation plays an important role in tumor progression and clinical outcomes. This study aimed to evaluate the association between preoperative systemic inflammatory indices and tumor burden, perioperative outcomes, and recurrence risk in patients with HGSOC undergoing primary debulking surgery. Methods: We conducted a retrospective study including 125 patients with histopathologically confirmed HGSOC who underwent primary debulking surgery between January 2020 and December 2025. Preoperative hematological parameters obtained within 24 h before surgery were used to calculate inflammatory indices including the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), lymphocyte-to-monocyte ratio (LMR), systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), and aggregate index of systemic inflammation (AISI). Associations between inflammatory markers, clinicopathological characteristics, perioperative outcomes, and recurrence were analyzed using non-parametric tests and logistic regression models. Results: The mean patient age was 53.66 ± 9.14 years, and most patients presented with advanced disease (FIGO III–IV: 70.4%). Patients with T3 tumors showed significantly higher monocyte (0.66 vs. 0.50 × 109/L, p = 0.003), neutrophil (5.43 vs. 4.99 × 109/L, p = 0.042), and platelet counts (325 vs. 280 × 109/L, p = 0.006) and lower lymphocyte counts (1.79 vs. 1.96 × 109/L, p = 0.009). Composite inflammatory indices were also increased in advanced disease, including PLR (177 vs. 153, p = 0.009), AISI (492 vs. 341, p = 0.002), and SIRI (1.65 vs. 1.18, p = 0.018). Patients requiring postoperative blood transfusion had higher neutrophil counts (7.65 vs. 4.97 × 109/L, p < 0.001) and elevated SIRI (2.56 vs. 1.55, p < 0.001). Patients with recurrence had significantly higher platelet counts (339 vs. 293 × 109/L, p = 0.001) and SII values (2849 vs. 2586, p = 0.012). In multivariate analysis, SII remained independently associated with recurrence (OR 1.022 per 100-unit increase; 95% CI 1.002–1.043; p = 0.033) together with advanced FIGO stages (OR 2.863; 95% CI 1.011–8.104; p = 0.048). Conclusions: Preoperative systemic inflammatory markers are significantly associated with tumor burden, surgical outcomes, and recurrence risk in HGSOC. An elevated SII appears to be an independent predictor of recurrence and may represent a practical biomarker for improving preoperative risk stratification and postoperative surveillance.