Mesotheliomas form a spectrum of tumors that usually arise in the pleura or in the abdominal cavity. The malignant tumors arising within the pleura are strongly associated with prior asbestos exposure in up to 90% of cases. The time period from initial exposure to development of the cancer may range from 25-45 years and the lifetime risk of developing mesothelioma following heavy exposure ranges from 7-10%. It diffusely spreads through the pleural space, directly invading other thoracic structures and associated with pleural effusion. The underlying lung is usually encased within the tumor.
The abdominal peritoneal variant is also related to asbestos exposure and 50% of these patients may have pulmonary fibrosis. Although 50% of these cases may be limited to the abdominal cavity, intestinal obstruction is common frequently leading to death.
The classic histopathology of the mesothelioma is a biphasic tumor with both an epithelioid and sarcomatoid or spindle cell component. From this description, it can be readily appreciated how the diagnosis may be very difficult to confirm. The table below lists the major histologic variants of the tumor. The task of the pathologist is to separate the mesothelioma from its many mimics including adenocarcinoma from the lung (in pleural cases) and soft tissue sarcomas such as malignant fibrous histiocytoma (in peritoneal cases). Immunoperoxidase studies and electron microscopy may aid in this distinction.
Unfortunately, the disease has a progressively downhill course. The importance in making the correct diagnosis is more of a medicolegal issue, because of the association of asbestos exposure, rather than a therapeutic one.
