Prognostic Role of PD-L1 Expression in Renal Cell Carcinoma. A Systematic Review and Meta-Analysis

Background: Several clinical trials have reported that therapies targeting programmed death-1 (PD1) and its ligand (PD-L1) improve patient outcomes, while tumor response has been related to PD-L1 expression. Objective: To investigate the prognostic role of PD-L1 expression in patients affected by renal cell carcinoma (RCC). Methods: MEDLINE/PubMed, the Cochrane Library, and ASCO University were searched for studies investigating the prognostic role of PD-L1 expression in RCC. Data extraction was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Results: Six studies and 1323 cases were included in the final analysis. PD-L1 was expressed in 24.2 % of clear cell tumors compared to 10.9 % of non-clear cell tumors (p = 0.002). In the overall population, a higher level of PD-L1 expression increased the risk of death by 81 % (HR; 1.81, 95 % CI 1.31–2.49; p < 0.001). When the analysis was restricted to cases evaluated by immunohistochemistry alone, the higher expression of PD-L1 more than doubled the risk of death (HR; 2.05, 95 % CI 1.38–3.05; p < 0.001). In clear cell histology, higher PD-L1 expression increased the risk of death by 53 % (HR; 1.53, 95 % CI 1.27–1.84; p < 0.001), while in metastatic patients, the evaluation of PD-L1 expression on primary tumors revealed that it retains its prognostic role (HR; 1.45, 95 % CI 1.08–1.93; p = 0.01). Limitations: Significant heterogeneity has been identified among the included studies. As a consequence, cautious interpretation of the results is recommended. Conclusion: This meta-analysis indicates that a higher level of PD-L1 expression is a negative prognostic factor in RCC. Its validation as an independent prognostic factor compared to other traditionally used clinical parameters in localized or advanced disease is recommended.[Figure not available: see fulltext.]