Putative Malignant Pleural Mesothelioma in situ (MPMIS) with Sequential Acquisition of Genomic Alterations on Fluorescence in situ Hybridization (FISH) Examination

Malignant pleural mesothelioma (MPM) is a rare and deadly disease. A precursor in situ lesion, malignant pleural mesothelioma in situ (MPMIS), has recently been proposed. On cytological examination, the distinction between reactive and malignant mesothelial cells is often challenging, and sometimes even impossible without ancillary methods. Fluorescence in situ hybridization (FISH) for detection of 9p21 deletion is a powerful diagnostic tool in this context, both in histological and in cytological specimens. Here, we present a case of MPM with initial presentation as a putative MPMIS with disomic chromosomal pattern and homozygous 9p21 deletion with subsequent development of an aneuploid pattern after whole genome duplication during tumor progression.

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.