State-of-the-art cytology of pleural fluid, focusing on the diagnosis of mesothelioma.

Mesothelioma has always been a challenging diagnosis to render in body cavity cytology samples. This review is a timely update on pleural fluid cytology and ancillary studies that should be considered in the diagnosis of mesothelial proliferations, specifically mesotheliomas. Information about new diagnostic approaches and ancillary studies in mesothelioma was obtained from the peer-reviewed literature and the authors' experiences. Although the morphological diagnosis of mesothelioma is fraught with numerous challenges given the overlap with other diagnostic entities, there are a variety of immunohistochemical and fluorescence in situ hybridization studies available to help in determining mesothelial origin and in distinguishing malignant proliferations from the more common benign or reactive mesothelial proliferations. Although ancillary studies can be helpful, there are important pitfalls to be aware of when interpreting these cases, and this review highlights some of the challenges that require caution.