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Mesothelioma : Cytologic Diagnosis

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The recurrent serous effusions caused by mesotheliomas are often submitted to the laboratory for analysis. Given the broad morphologic overlap between reactive mesothelial cells and malignant mesothelial cells, the cytologic diagnosis of mesothelioma is extremely challenging and has a reported sensitivity of between 32% and 76%. It is important to remember that sarcomatoid mesotheliomas don't shed cells into effusions and are almost never diagnosed on cytology. Such cases, on the contrary, may contain reactive mesothelial cells misleading the pathologist.

The image shows malignant mesothelioma in a pleural fluid specimen. Useful diagnostic features include: numerous large balls of cells (>50 cells) with berry-like external contours; cellular enlargement with more abundant cytoplasm; large nuclei with macronucleoli; nuclear anaplasia, when present. Immunohistochemical and molecular techniques can be applied on cell blocks and smears to greatly improve the diagnostic yield. About 70% of mesothelial proliferations contain homozygous deletion of p16 which can be demonstrated by FISH technique. Likewise, positive desmin and negative EMA by immunohistochemistry strongly favors a reactive process and a reverse profile (desmin-ve, EMA+ve) strongly favors malignant mesothelioma (Ref: Hasteh F et al. Cancer Cytopathol 2010;118:90-6.) Photograph copyright 2011 Nephron. This image is used under the terms of GNU Free Documentation License Version 1.2

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