Mesothelioma is a rare form of cancer that is well known to some industrial workers: when it does occur it is usually in people who have been exposed to asbestos in their work. Asbestos workers who are also smokers are particularly at risk. Industrial laws that protect asbestos workers from this hazard have kept this as an uncommon cancer. Mesothelioma is not truly a cancer of the lung but is a cancer of the tissues surrounding and lining the lungs (the pleura). It may rarely occur in other lining tissues such as the lining of the abdominal cavity (the peritoneum). Mesothelioma patients may seek treatment for a cough, chest infection, difficulty with breathing or chest pain. A tumor lump may be felt or seen on an X -ray or CT scan. Meso-thelioma is difficult to treat, as it is usually too widespread and advanced to treat by surgery and does not usually respond well to either radiotherapy or chemo. The best treatment is often simply to give the patient best relief from symptoms while the tumor progresses slowly.

Scholarly Information--Mesotheliomas are primary tumors arising from the surface lining of the pleura (80% of cases) or peritoneum (20% of cases). About three-fourths of pleural mesotheliomas are diffuse (usually malignant) tumors, and the remaining one-fourth are localized (usually benign). Men out number women by a 3:1 ratio. Numerous studies have confirmed the association of malignant pleural mesothelioma with exposure to asbestos (particularly the crocidolite form). The lifetime risk to asbestos workers of developing malignant pleural mesothelioma is about 8%. The clinician should inquire about asbestos exposure through mining, manufacturing, shipyard work, insulation, brake linings, building construction and demolition, roofing materials. and a variety of asbestos producers (pipe, textiles, paint, tile, gaskers, panels). Sixty to 80 percent of patients with malignant mesothelioma report a history of asbestos exposure. Although cigarette smoking significantly increases the risk of bronchogenic carcinoma in asbestos workers and aggravates asbestosis, there is no association between smoking and mesothelioma.

The mean age at onset of symptoms of malignant pleural mesothelioma is about 60 years. The latent period between exposure and onset of symptoms ranges from 20 to 40 years. Symptoms include the insidious onset of shortness of breath, nonpleuritic chest pain, and weight loss. Physical findings include dullness to percussion, diminished breath sounds, and, in some cases, finger clubbing. Radiographic abnormalities consist of nodular, irregular, unilateral pleural thickening and varying degrees of unilateral pleural effusion. CT scan helps demonstrate the extent of pleural involvement.

Pleural fluid is exudative and often hemorrhagic. Open pleural biopsy is usually necessary to obtain an adequate specimen for histologic diagnosis; even then, distinction from benign inflammatory conditions and from metastatic adenocarcinoma may be difficult. The histologic variants of malignant pleural mesothelioma are epithelial and fibrous (sarcomatous). Special stains and electron microscopy may be needed to confirm the diagnosis.

Malignant pleural mesothelioma progresses rapidly as the tumor spreads quickly along the pleural surface to involve the pericardium, mediastinum, and contra lateral pleura. The tumor may eventually extend beyond the thorax to involve abdominal lymph nodes and organs. Progressive pain and dyspnea are characteristic. Median survival time from onset of symptoms ranges from 5 months in extensive disease to 16 months in localized disease, and about 75% of patients are dead within 1 year after diagnosis. Treatment with surgery, radiotherapy, chemotherapy, and a combination of methods has been attempted but is generally unsuccessful. Some surgeons believe that extrapleural pneumonectomy is the preferred surgical approach for patients with early stage disease. Drainage of pleural effusions, pleurodesis radiation therapy, and even surgical resection may offer palliative benefit in some patients.

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