Sarcomatoid mesothelioma vs. myogenic sarcoma: a strong case for diagnostic electron microscopy: a case report.

Mesothelioma is often considered a difficult diagnosis due to its rarity, the wide variety of histological patterns and the propensity of metastasis from cancers of unknown origin to serosal surfaces. The advent of numerous new immunochemical markers has provided extensive aid in diagnosing epithelial mesotheliomas. However, immunochemical markers that assist in the diagnosis of sarcomatoid mesothelioma remain limited. Sarcomatoid mesothelioma is the most aggressive and least common form of mesothelioma. Therefore, sarcomatoid mesothelioma diagnosis has the added challenge of increased rarity in addition to a lack of distinctive immunochemical features. Electron microscopy (EM) is a useful tool for visualizing the ultrastructural components of different tumors and has been utilized to identify distinctive features in the diagnosis of epithelial mesotheliomas. Utilization of EM in cases of sarcomatoid mesotheliomas has been limited due to a lack of diagnostic ultrastructural markers. However, EM can still be useful in evaluation of sarcomatoid tumors when sarcomatoid mesotheliomas are part of the differential diagnosis. Here, we present the case of an individual with suspected sarcomatoid mesothelioma and demonstrate the utility of EM in differentiating alternative sarcomatoid malignancies, namely a myogenic sarcoma, by identifying diagnostic ultrastructural components.