Mesothelioma

Fritz J. Baumgartner

Mesothelioma is a primary tumor of the pleura. Most pleural tumors are actually not primary but rather metastatic from other primary sites such as breast or lung. The few primary tumors that do arise from the pleura are usually malignant. There is a strong causal relationship between asbestos exposure and mesothe-lioma. Nonetheless, only 7% of people exposed to asbestos actually develop mesothelioma. On the other hand, 50% of patients who have mesothelioma have history of exposure to asbestos. There is characteristically a long period of time between exposure and development of the tumor. The increased risk occurs 20 years after the first exposure and continues to rise for many years thereafter.

There are two types of mesothelioma—localized and diffuse. Diffuse mesotheliomas are nearly always malignant, however localized mesotheliomas may be either benign or malignant. About 30% of localized mesotheliomas are malignant and 70% benign. Benign pleural mesotheliomas usually arise from the visceral pleura on a stalk and project into the pleural space, although sessile attachment to the pleura may also occur. The tumor may also arise from the parietal pleura. Patients with localized malignant lesions usually have symptoms compared to patients with localized benign lesions; these include cough, pain, fever, and shortness of breath.

Mesothelioma may produce a bloody pleural effusion. In this case, a complete resection of the lesion may still be possible even if it is associated with a bloody effusion. This is an important distinction between a mesothelioma and an intra-thoracic lung neoplasm associated with a bloody pleural effusion. For a lung tumor, a pleural effusion which is bloody usually means an inoperable T4 lesion unlike mesothelioma.

Solitary mesotheliomas are usually asymptomatic. Benign localized mesothe-lioma is also accompanied by hypertrophic pulmonary osteoarthropathy. A large tumor may be associated with severe hypoglycemia as well. Hypertrophic pulmonary osteoarthropathy occurs in about half of patients with mesothelioma, compared with 5% of patient with bronchogenic carcinoma.

Clubbing of the fingers and toes may also occur with mesothelioma, and is different from hypertrophic pulmonary osteoarthropathy. Clubbing results from new periosteal growth with lymphocytic infiltration of the nail beds. Whereas lung and pleural tumors may cause clubbing, benign causes include cyanotic heart disease, endocarditis, AV fistula, lung infection, COPD and sarcoid.

Treatment of localized benign mesothelioma is surgical resection, with good results. Treatment of the localized malignant variety is wide local excision, including adjacent chest wall if arising from parietal pleura.

In diffuse malignant mesothelioma, any portion of the pleura may be involved. It typically appears as sheets of tumor. Hematogenous spread to distant organs occurs in half. The symptoms include dyspnea, weight loss, cough and pain which is often severe. A pleural effusion is present in most of these patients. Diagnosis is achieved with needle pleural biopsy and thoracentesis. The treatment of diffuse mesothelioma is nearly always only palliative. However, radiation and chemotherapy have only been inconsistent in achieving this goal. Surgery in this disease is controversial. Seeding is frequent, and tumor may actually grow out of the thoracotomy incision used to treat the tumor. Some say surgery should be limited to achieving a diagnosis. Others advocate thoracotomy with pleurectomy whereas others perform a radical extrapleural pneumonectomy to remove all the pleura and lung on the affected side. Although 2 year survival after the procedure is improved with up to one-third surviving, 5 year survival is dismal.

Suggested Reading

1. Rusch VW et al. Pleurectomy/decortication and adjuvant therapy for malignant mesothelioma. Chest 1993; 103: 382S.

2. Rusch VW, Venkatraman E. The importance of surgicla staging in the treatment of malignant pleural mesothelioma. J Thorac Cardiovasc Surg 1996; 111:815.

3. Sugarbaker DJ et al. Extrapleural pneumonectomy in the multimodality therapy of malignant pleural mesothelioma. Results in 120 consecutive patients. Ann Surg 1996; 224:288.

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