PD-L1 expression associated with worse survival outcome in malignant pleural mesothelioma

There is currently a need to identify prognostic biomarkers to assist in a risk adopted approach in treatment of malignant pleural mesothelioma (MPM). Expression of programmed death ligand 1 (PD-L1) has been studied as a prognostic biomarker in a number of tumors given its central role in antitumoral immune response evasion. Four previously published analyses found PD-L1 positivity to be an adverse survival prognostic factor in MPM. This study aims to further investigate the relationship between PD-L1 expression in mesothelioma tissues and survival outcome.

Clinical data of MPM patients from a single institution between 2006 and 2016 were reviewed. Patient's archived tissues were stained with PD-L1 (Clone Ventana SP263). PD-L1 positivity was defined as > 1% membranous staining regardless of intensity.

Data from fifty eight patients were analyzed. Median age was 73, majority was male (49, 84%) and had ECOG between 0 and 2 (46, 79%). Most common histopathological subtype was epithelioid (42, 72%), 9 (16%) biphasic subtype and 7 (12%) sarcomatoid. Thirty one patients (53%) received best supportive care and twenty seven patients (47%) received chemotherapy or combination treatment. Forty-two patients had positive PD-L1 expression (72.4%). The median survival time for PD-L1 negative group is 15.5 months and 6 months for the positive group. Positive PD-L1 expression is independently correlated with worse prognosis (HR = 2.02; 95% CI, 1.005-4.057; P-value = 0.0484).

Our analysis found a higher percentage of MPM patients with positive PD-L1 (> 1%) compared to other studies. Highly positive PD-L1 expression was associated with statistically significantly lower median survival time.