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Extensive Emperipolesis of Neoplastic Lymphocytes by Mesothelial Cells in Pleural Effusion Cytology in a Case of a Mediastinal T-Cell Lymphoblastic Lymphoma: A Rare but Diagnostically Useful Phenomenon

Emperipolesis is a biological process defined by the presence of an intact cell within the cytoplasm of another cell. In pleural fluid cytology, the phenomenon is very rare but has already been described in B-cell lymphoma. Here, we report the first case of a T-cell lymphoma diagnosed on a pleural fluid exhibiting extensive emperipolesis of tumor cells by mesothelial cells. Additionally, in order to evaluate the prevalence of emperipolesis in lymphocyte rich pleural effusion cytology, we reviewed cases from our archive, including cases with lymphoma and cases with reactive T-lymphocyte rich effusion.