BACKGROUND

The prognostic role of programmed cell death 1 ligand 1 (PD-L1) in malignant pleural mesothelioma (MPM) is incompletely understood. Our objectives were to evaluate the evidence for tumor PD-L1 as a prognostic biomarker in MPM through meta-analysis and to determine whether tumor PD-L1 expression is associated with survival in MPM patients undergoing macroscopic complete resection.

METHODS

Meta-analysis was performed to determine the association of PD-L1 with overall survival in MPM (n = 1655) from 14 studies containing overall survival and tumor PD-L1 expression. Univariable and multivariable analyses tested the relationship of tumor PD-L1 with overall survival and recurrence-free survival in an institutional cohort of MPM patients treated by macroscopic complete resection (n = 75). To validate the association of PD-L1 with overall survival, we utilized two independent MPM cohorts (n = 284).

RESULTS

Meta-analysis demonstrated that high tumor PD-L1 expression was associated with poor overall survival. Among 75 patients undergoing macroscopic complete resection, 49 tumors (65%) expressed PD-L1 (1% or more), and high PD-L1 (50% or greater) was more commonly expressed on nonepithelial (29%) compared with epithelial tumors (14%). High tumor PD-L1 expression was independently associated with poor overall survival (P < .001, hazard ratio 5.67) and recurrence-free survival (P = .003, hazard ratio 3.28). The association of PD-L1 overexpression with unfavorable survival was more significant in epithelial MPMs than nonepithelial MPMs. These findings were validated in RNA sequencing analyses in two independent cohorts. Exploratory transcriptome analysis revealed that MPM tumors with PD-L1 overexpression displayed coexpression of other immune regulatory molecules, programmed cell death 1 ligand 2 and T-cell immunoglobulin mucin receptor 3.

CONCLUSIONS

Tumor PD-L1 expression is a prognostic biomarker in patients undergoing surgical resection for MPM and may be useful in perioperative decision making.