Background: Types: Pleural mesothelioma (~85%) Peritoneal mesothelioma (~15%) Histology: Epithelioid Mesothelioma: Epithelioid-to-round cells Better prognosis Non-Epithelioid Mesothelioma: Sarcomatoid: Spindle cells with tapered nuclei Biphasic: Contains both epithelioid and sarcomatioid components in various proportions (each at least 10% of the tumor) Diagnosis: Immunohistochemical panels are essential for diagnosis, requires both criteria: 2 positive mesothelial markers: