BackgroundAll malignant tumors may spread throughout the pleural, peritoneal, and pericardial cavities. The presence of tumor cells in serosal fluid is a poor prognostic indicator. It may be difficult to differentiate nuclear atypia of mesothelial cells due to injury of serosal surfaces from mesothelioma or malignant epithelial tumor cells. Epithelial and mesothelial immunohistochemical markers can be used in such conditions. The aim of this study was to evaluate the expression of two immunohistochemical markers (MOC-31 and EZH2) in serosal effusions.