Clinical Value of an LDH–CA125–NLR Panel for Diagnosis, Platinum Resistance, and Prognostic Assessment in Epithelial Ovarian Cancer

(1) Background/Objective: Routine blood tests may provide useful information at different stages of epithelial ovarian cancer (EOC) management. This study evaluated continuous lactate dehydrogenase (LDH), carbohydrate antigen 125 (CA125), and neutrophil-to-lymphocyte ratio (NLR) values for diagnostic discrimination in epithelial ovarian cancer (EOC) and, separately, triple-positive status in relation to platinum resistance and survival. (2) Methods: This retrospective study included 238 patients with EOC and 238 individually matched patients with benign ovarian lesions. Continuous biomarkers were entered into logistic regression models for diagnosis. Triple-positive status was defined as LDH > 195.5 U/L, CA125 > 35.37 U/mL, and NLR > 2.63. Logistic regression was used for platinum resistance and Cox regression for progression-free survival (PFS) and overall survival (OS). Bootstrap internal validation was performed for the diagnostic models and PFS nomogram. (3) Results: The continuous LDH + CA125 + NLR model yielded an AUC of 0.873, with 75.97% sensitivity and 88.66% specificity; AUCs were 0.751 in early-stage and 0.958 in advanced-stage EOC. Adding NLR to LDH + CA125 did not significantly improve the AUC overall or within stage groups. Triple-positive status was associated with platinum resistance (adjusted OR = 3.488, 95% CI 1.504–8.087; p = 0.004), shorter PFS (adjusted HR = 3.109, 95% CI 1.772–5.456; p < 0.001), and shorter OS in advanced-stage EOC (adjusted HR = 3.538, 95% CI 1.385–9.038; p = 0.008). The PFS nomogram had a bootstrap-corrected C-index of 0.7521. (4) Conclusions: The continuous three-marker model showed diagnostic discrimination in this selected surgical cohort, while triple-positive status was associated with platinum resistance and adverse survival outcomes. External validation is needed.