Malignant pleural effusion (MPE) confers dismal prognosis and has limited treatment options. While immune-checkpoint inhibition (ICI) proved clinical efficacy in a variety of malignancies, data on the prognostic role of PD-L1 in MPE is scarce. We retrospectively studied PD-L1 tumour proportion score and Ki-67 index in pleural biopsies or cytologies from 123 patients (69 lung cancer, 25 mesothelioma, and 29 extrathoracic primary malignancies). Additionally, the impact of C-reactive protein (CRP) and platelet count was also analysed. Median overall survival (OS) after MPE diagnosis was 9 months. Patients with PD-L1 positive tumours (≥1%) had significantly shorter OS than patients with negative PD-L1 status (p = 0.031). CRP and Ki-67 index were also prognostic and remained independent prognosticators after multivariate analysis. Interestingly, Ki-67 index and CRP influenced the prognostic power of PD-L1. Finally, patients receiving ICI tended to have a longer median OS and CRP - but not PD-L1 - was a significant prognosticator in this subgroup. In summary, histological and circulating biomarkers should also be taken into account as potential biomarkers in ICI therapy and they may have an impact on the prognostic power of PD-L1. Our findings might help personalizing immune-checkpoint inhibition for patients with MPE and warrant further prospective validation.

Malignant pleural mesothelioma (MPM) is an aggressive disease with limited treatment response and devastating prognosis. Exposure to asbestos and chronic inflammation are acknowledged as main risk factors. Since immune therapy evolved as a promising novel treatment modality, we want to reevaluate and summarize the role of the inflammatory system in MPM. This review focuses on local tumor associated inflammation on the one hand and systemic inflammatory markers, and their impact on MPM outcome, on the other hand. Identification of new biomarkers helps to select optimal patient tailored therapy, avoid ineffective treatment with its related side effects and consequently improves patient’s outcome in this rare disease. Additionally, a better understanding of the tumor promoting and tumor suppressing inflammatory processes, influencing MPM pathogenesis and progression, might also reveal possible new targets for MPM treatment. After reviewing the currently available literature and according to our own research, it is concluded that the suppression of the specific immune system and the activation of its innate counterpart are crucial drivers of MPM aggressiveness translating to poor patient outcome.

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