PD-L1 EXPRESSION AND SERUM CA125: CLINICOPATHOLOGICAL CORRELATIONS IN HIGH-GRADE SEROUS OVARIAN CARCINOMA.

INTRODUCTION: Programmed death-ligand 1 (PD-L1) has emerged as an important immune checkpoint biomarker in ovarian cancer. However, its relationship with serum cancer antigen 125 (CA125), a routinely used biomarker for disease monitoring, remains insufficiently investigated, particularly in patients with high-grade serous ovarian carcinoma (HGSC). AIM: To evaluate the association between PD-L1 expression and serum CA125 levels in patients with high-grade serous ovarian carcinoma and to investigate the relationships of PD-L1 expression with age and FIGO stage. MATERIALS AND METHODS: This retrospective case-control study included 69 women treated for ovarian tumors between 2018 and 2025, comprising 42 patients with histologically confirmed HGSC and 27 patients with benign epithelial ovarian tumors serving as controls. PD-L1 expression was assessed immunohistochemically using the VENTANA PD-L1 (SP263) assay and evaluated by the Tumor Proportion Score (TPS), with positivity defined as TPS ≥1%. Serum CA125 levels were categorized as ≤35 U/mL or >35 U/mL. Statistical analyses included Pearson's chi-square test, Fisher's exact test, and odds ratios (ORs) with 95% confidence intervals (CIs), with statistical significance defined as p<0.05. RESULTS: PD-L1 expression was detected in 17 (24.6%) of the 69 patients, including 16/42 (38.1%) patients with HGSC and 1/27 (3.7%) controls. PD-L1 positivity was significantly more frequent in HGSC than in benign tumors (OR=16.0; 95% CI 1.97-129.64; p=0.0012). Within the HGSC cohort, CA125 >35 U/mL was observed in 13/16 (81.3%) PD-L1-positive and 22/26 (84.6%) PD-L1-negative patients. No significant association was identified between CA125 category and PD-L1 expression (OR=0.79; 95% CI 0.15-4.09; Fisher's exact p=1.000). No statistically significant associations were observed between PD-L1 expression and age (p=0.454) or FIGO stage (p=0.978). CONCLUSION: PD-L1 expression was significantly more frequent in HGSC than in benign epithelial ovarian tumors. However, the initially observed association between PD-L1 expression and elevated serum CA125 was not confirmed when the analysis was restricted to the 42-patient HGSC cohort. Larger studies are needed to clarify the relationship between PD-L1 and CA125 within HGSC.