Ref:Textbook of pathology (Harsh mohan) 6th edition,page no.505 Mesothelioma is an uncommon tumour arising from mesothelial lining of serous cavities, most often in pleural cavity, and rarely in peritoneal cavity and pericardial sac. Mesotheliomas are of 2 types--benign (solitary) and malignant (diffuse). The biologic behaviour of pleural mesotheliomas is usually predicted by their gross appearance--those forming solitary, discrete masses are generally benign, whereas those which grow diffusely are usually malignant. Benign (Solitary) Mesothelioma Benign or solitary mesothelioma is also called as pleural fibroma. Asbestos exposure plays no role in etiology of benign mesothelioma. Malignant (Diffuse) Mesothelioma Malignant or diffuse mesothelioma is rare. It is a highly malignant tumour associated with high moality. The tumour is significant in view of its recognised association with occupational exposure to asbestos Pleural fibroma is differentiated from mesothelioma by the presence Cytokreatin