Cytology is usually the first step in investigating serous effusions, to either detect or exclude an underlying malignancy. This study will try to answer the need for improved diagnostic yield of cytologic examination by cell block technique and immunohistochemical testing of three markers which are EZH2, Claudin-4 and MOC-31.

This is a prospective study that will be conducted at the pathology lab of Assiut University Hospital. The study will include effusion specimens (pleural, peritoneal & pericardial) and the aspirated fluid will be examined for physical characters e.g. color and appearance.

The sample will be divided into 2 equal parts: one for conventional smear preparation, and the other for cell block. A minimum of 2 thin smears will be prepared and stained with Papanicolou stain.

Cell block sections of 4-6 μ thickness will be prepared and stained with the hematoxylin and eosin stain (H&E).

For immunohistochemistry, cell blocks will be used. Expression of claudin 4, EZH2, and MOC-31 will be evaluated in benign and malignant cells by using immunoperoxidase technique.

Inclusion Criteria:

• all cases with serous effusion of unknown aetiology including ascites, pleural or pericardial effusions.

Exclusion Criteria:

• No exclusion criteria from the histopathologist perspective, i.e. all cases that undergone diagnostic aspiration are eligible for the study.

all cases that have serous effusion of undiagnosed underlying aetiology.