الفهرس 
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Abstract
Malignant epithelioid mesothelioma cells in effusions may have cytological features like RMCs and lung adenocarcinoma cells. The lack of definite cytological criteria that correspond to the detection of invasion in histological sections may also cause some pathologists to be reluctant to make a conclusive diagnosis of MPM.
However, several antibodies and panels with different sensitivity and specificity have been proposed, no gold standard has been established. So, it is mandatory to search for new diagnostic markers that could facilitate early diagnosis and differentiating lung adenocarcinoma from MPM in effusion cytology; among these are HEG1 and Claudin-4.
This work aims to evaluate the role of HEG1 and Claudin-4 IHC staining in differentiating MPM from lung adenocarcinoma in pleural effusion cytological specimens.
The protein HEG 1 is a mesothelioma-related antigen. It is believed to control the endothelial cell signaling pathway. The survival and growth of mesothelioma cells are aided by HEG1 expression.
Claudin-4 is a tight-junction-associated protein. It has been shown to be widely expressed in normal and malignant epithelial cells, but Claudin-4 is absent in normal and malignant mesothelium.
Eighty-four samples of pleural effusions were collected from the Chest and Cardiothoracic Surgery Departments, Faculty of Medicine; Zagazig University. The cases were 20 cases of benign effusions with RMCs, 25 cases of MPM and 39 cases of lung adenocarcinoma. Cytological examination of pleural aspirate was done by routine H&E stained smears, followed by formation of cell block. Three to five micrometer thick sections of each cell block were done. One section was stained by H&E for histopathological evaluation and other sections for HEG1 and Claudin-4 IHC staining evaluation.
Positive membranous HEG1 immunoexpression was found in 95% cases of RMCs of benign effusions. Also, positive membranous HEG1 immunoexpression was found in 96% of cases of MPM, and only 2.6% of lung adenocarcinoma cases. There was a statistically significant difference between benign effusion with RMCs and lung adenocarcinoma immunoreactivity (p. value <0.001). There was highly statistical significant difference between HEG1 immunoexpression in MPM and lung adenocarcinoma (p. value <0.001). There was no statistically significant difference in immunoexpression of HEG1 between benign effusion with RMCs and MPM.
All cases of benign effusions with RMCs and all cases of MPM were negative reactivity for Claudin-4 immunoexpression while positive membranous Claudin-4 immunoexpression was found in 94.9% of lung adenocarcinoma cases. In the present study, there was statistically significant difference in immunoexpression of Claudin-4 between benign effusion with RMCs and lung adenocarcinoma (p. value <0.001). There was statistically significant difference in immunoexpression of Claudin-4 between MPM and lung adenocarcinoma (p. value <0.001). There was no statistically significant difference in the immunoexpression of Claudin-4 between benign effusion with RMCs and MPM.