Diffuse Biphasic Mesothelioma in a Patient Initially Misdiagnosed as Sarcomatoid Carcinoma: Case Report and Review of the Literature

Abstract

Diffuse Mesothelioma (DM) is an uncommon, aggressive malignant tumor of the mesothelial cells of the pleura, peritoneum, pericardium, and testicular tunica vaginalis. DM is historically associated with occupational asbestos exposure, and the latent period can be up to 40 years or more. The main histological types of DM are diffuse epithelioid Mesothelioma (DEM), diffuse sarcomatoid Mesothelioma (DSM), and diffuse biphasic Mesothelioma (DBM). According to the 2021 WHO classification of tumors of the pleura, the presence of >10% of each of the epithelioid and sarcomatoid patterns in definitive resection specimens or any percentage of each component in small biopsy and cytology specimens is sufficient to make the diagnosis of diffuse biphasic Mesothelioma (DBM). However, a definitive diagnosis of DBM in small tissue samples can be challenging and lead to an incorrect diagnosis. Considering the legal impact of a diagnosis of DM, optimal diagnosis requires a comprehensive panel of immunohistochemistry (IHC) studies and confirmatory molecular testing. We report a case of a 69-year-old woman with a history of asbestos exposure who presented with multiple pleural, pericardial, and peritoneal plaques and was initially misdiagnosed as sarcomatoid carcinoma. A comprehensive panel of IHC studies and molecular testing confirmed the diagnosis of DBM.