Prognostic value and clinical significance of tumoral PD-L1 and stromal α-SMA expression in diffuse pleural mesothelioma.

Diffuse pleural mesothelioma (PM) is a rare malignant neoplasm with an extremely poor prognosis. Prognostic assessment remains challenging, highlighting the urgent need for reliable biomarkers to guide precise and effective therapy. Programmed death ligand 1 (PD-L1) has been suggested as a predictive biomarker for PM, but existing data are limited and controversial. Although advances have been made in understanding cancer-associated fibroblasts (CAFs) within the PM tumor microenvironment, their clinical and prognostic significance remains poorly elucidated. A retrospective analysis of 51 pathologically diagnosed PM was performed. We evaluated clinicopathological factors (including tumoral PD-L1, stromal α-SMA, and Ki-67 percentage by immunohistochemistry) and analyzed their correlation with overall survival (OS) using Kaplan-Meier and multivariate Cox regression. A total of 12 potential prognostic factors were evaluated in the univariate analysis, and 6 factors were found to be significantly associated with a poor prognosis in PM patients. Multivariate analysis identified histological classification, TNM stage, and PD-L1 expression as independent prognostic factors in PM patients. Stromal α-SMA positivity, a marker of poor prognosis, was significantly correlated with male, non-epithelioid subtype, and a high Ki-67 index. Moreover, α-SMA positivity tended to show an increased likelihood of PD-L1 expression (p=0.065). The expression of tumor PD-L1 could serve as an adverse prognostic factor for PM patients. Its potential association with tumor stromal α-SMA expression warrants further investigation, particularly in the context of unmet needs in tumor immunotherapy.