Detection of EpCAM-positive microparticles in pleural fluid: A new approach for the diagnosis of the tumoral origin of pleural effusions

Background: Pleural biomarkers are needed for the diagnosis of malignant pleural effusion at an early stage before true carcinomatosis. Tumor cells produce microparticles, and, therefore, we hypothesized that tumor-derived microparticles could be present in the pleural liquid and could help to identify patients with malignant pleural effusions by a non-invasive method. Methods: Fifty patients with benign (n=11) or malignant (n=39) pleural effusions were included in this study. Among them, 39 consecutive patients with histologically shown primary or metastatic pleural cancer were included. After the optimization of a sample processing protocols, MPs were enumerated by flow cytometry and the Cryo-Transmission Electron Microscopy was performed. Measurement of EpCAM-positive MPs was analyzed by ELISA. Results: Using highly sensitive flow cytometry and cryo-electron microscopy, this study showed the presence of microparticles in pleural effusions. We demonstrated the presence of tumor-derived microparticles expressing EpCAM (epithelial-cell-adhesion-molecule) in the pleural fluids from adenocarcinoma patients. In our cohort, the detection of EpCAM-positive microparticles was shown to be useful as a tool to complement cytology for better diagnoses of malignant pleurisies. Conclusions: To our knowledge, this is the first work to directly identify tumoral microparticles in pleural liquids using EpCAM. The identification of EpCAM+ microparticles could lead to a new diagnostic and monitoring approach. This study establishes the basis for a potential biomarker for diagnosing and monitoring malignant pleurisy.