Prognostic value of programmed death-ligand 1 (PD-L1) expression in ovarian clear cell carcinoma

OBJECTIVE: Programmed death-ligand 1 (PD-L1) was expressed in various tumors and antibodies targeting its receptor programmed cell death-1 (PD-1) are emerging cancer therapeutics. This study was designed to evaluate the expression of PD-L1 and its correlation with clinicopathologic features and clinical outcomes in ovarian clear cell carcinoma (OCCC). METHODS: The PD-L1 expression was measured by tissue-microarray-based immunohistochemistry from 122 eligible patients diagnosed with OCCC. The associations of clinicopathologic features with progression-free survival (PFS) and overall survival (OS) were analyzed by Kaplan-Meier method and multivariate analysis was further performed by Cox regression model. RESULTS: Overall, high PD-L1 expression (PD-L1(high)) was observed in 44.7% (55/123) of OCCC patients, and was strongly associated with advanced stages (p=0.020), positive ascitic fluid (p=0.016), platinum-resistant (PR) disease (p=0.045), and recurrence (p=0.038). Moreover, patients with PD-L1(high) were associated with poorer OS (hazard ratio [HR]=2.877; p=0.001) and PFS (HR=1.843; p=0.021) than those with low PD-L1 expression (PD-L1(low)). In subgroup analysis, PD-L1(high) patients experienced a poorer PFS (HR=1.926; p=0.044) and OS (HR=2.492; p=0.021) than PD-L1(low) cases among advanced stages (III-IV), but this difference was not observed in stage I-II patients. Meanwhile, PD-L1(high) was associated with poorer prognosis than PD-L1(low) in PR patients (OS, HR=2.253; p=0.037; PFS, HR=1.448; p=0.233). Multivariate analysis revealed that PD-L1(high) and advanced stages (III-IV) were adverse independent prognosticators for both PFS (HR(PD-L1)=2.0; p(PD-L1)=0.038; HR(stage)=10.2; p(stage)<0.001) and OS (HR(PD-L1)=3.0; p(PD-L1)=0.011; HR(stage)=14.3; p(stage)<0.001). CONCLUSION: PD-L1(high) might serve as a risk factor for PFS and OS in patients with OCCC. It is possible that immunotherapy targeting PD-L1 pathway could be used in OCCC.