Low Neutrophil-to-Lymphocyte Ratio Combined with High Intraepithelial CD8+ Tumour-Infiltrating Lymphocytes Within the Tumour Microenvironment Is a Prominent Prognostic Factor in Advanced Epithelial Ovarian Cancer

Background/Objectives: Tumour-infiltrating lymphocytes (TILs) significantly influence the prognosis of epithelial ovarian cancer (EOC). Advanced EOCs often cause neutrophilia, ascites, and malnutrition. The neutrophil-to-lymphocyte ratio (NLR) serves as a marker of systemic inflammation. This study investigated the prognostic significance of pre-treatment NLR and TILs in advanced EOCs. Methods: Overall, 101 advanced EOCs (stages III–IV, FIGO 2014) were treated between 2005 and 2020. Based on pathological findings, advanced EOCs were classified as having high or low TILs using CD8 and CD4 immunostaining. The tumour proportion score was calculated to determine PD-L1 expression. The number of marker-positive cells was counted using HALO. Progression-free survival and overall survival (OS) were compared between the high- and low-NLR groups based on TILs levels. Results: Clinicopathological characteristics, including age, FIGO stage, histological subtype, and postoperative residual disease, did not significantly differ among the four groups defined by NLR and intra-epithelial CD8+ TILs (CD8+ iTILs). Multivariate analysis of OS revealed that NLR and CD8+ iTILs were independent prognostic factors, and no correlation was observed between them. The 5-year OS rates were 82.2% in the low NLR–high CD8+ iTILs group (n = 25), 41.7% in the low NLR–low CD8+ iTILs group (n = 16), 47.2% in the high NLR–high CD8+ iTILs group (n = 34), and 26.0% in the high NLR–low CD8+ iTILs group (n = 26). In the low-NLR subgroup, OS was significantly prolonged in the high CD8+ iTILs group (p = 0.023). Conclusions: In advanced EOCs, the status of tumour-localised immunity and pre-treatment systemic inflammation influenced long-term prognosis.