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Pleural mesothelioma is the only known pleural cancer and is caused by asbestos exposure in nearly all cases. Diagnosis is based on history and chest x-ray or CT findings and tissue biopsy. Treatment is supportive, which may require surgery, chemotherapy, or both.
Asbestos is a family of naturally occurring silicates whose heat-resistant and structural properties made it useful for inclusion in construction and shipbuilding materials, automobile brakes, and some textiles. Chrysotile (a serpentine fiber), crocidolite, and amosite (amphibole, or straight fibers) are the 3 main types of asbestos that cause disease.
Asbestos workers have up to a 10% lifetime risk of developing mesothelioma, with an average latency of 30 yr. Risk is independent of smoking. Mesothelioma can spread locally, or it can metastasize to the hilar and mediastinal lymph nodes, pericardium, diaphragm, peritoneum, liver, adrenals, or kidneys and, rarely, the tunica vaginalis of the testis.
The pleural form of mesothelioma, which represents > 90% of all cases (the other 10% include pericardial and peritoneal mesotheliomas), appears on x-ray as diffuse unilateral or bilateral pleural thickening that appears to encase the lungs, usually producing blunting of the costophrenic angles. Pleural effusions are present in 95% of cases and are typically unilateral, large, and hemorrhagic. Diagnosis is based on pleural fluid cytology or pleural biopsy. Increased levels of hyaluronidase in pleural fluid are suggestive but not diagnostic of mesothelioma. If diagnosis is uncertain after these procedures, biopsy by VATS or thoracotomy is done. Soluble mesothelin-related proteins released into the serum by mesothelial cells are being studied as possible tumor markers for disease detection and monitoring, but the false-positive rate may limit their effectiveness.
Staging is done with chest CT, mediastinoscopy, and MRI. Sensitivity and specificity of MRI and CT are comparable, although MRI is helpful in determining tumor extension into the spine or spinal cord. PET may have better sensitivity and specificity for distinguishing benign from malignant pleural thickening. Bronchoscopy should be done to exclude coexisting endobronchial lung cancers.
Mesothelioma remains an incurable cancer, and long-term survival is uncommon. Surgery to remove the pleura, ipsilateral lung, phrenic nerve, hemidiaphragm, and pericardium combined with chemotherapy or radiation therapy may be considered, although it does not substantially change prognosis or survival time. No treatment substantially prolongs survival. Median survival from time of diagnosis is 9 to 12 mo, depending on the location and cell type. A few patients, usually younger patients with shorter duration of symptoms, have a more favorable prognosis, sometimes surviving for several years after diagnosis.
The major focus of treatment is supportive care and relief of pain and dyspnea. Given the diffuse nature of the disorder, radiation therapy is usually unsuitable except to treat localized pain or needle-tract metastases. It is not generally used for treatment of nerve root pain. Pleurodesis or pleurectomy can be used to help reduce dyspnea caused by pleural effusions. Adequate analgesia is important but difficult to achieve. Usually, opioids, both transdermal and delivered via indwelling epidural catheters, are used.
Because morbidity and mortality are high with extrapleural pneumonectomy, pleurectomy and decortication are used increasingly if all grossly visible tumor can be removed. However, complete resection is usually not feasible. Nonsurgical therapies include chemotherapy (eg, with pemetrexed and a platinum compound) and radiation therapy. Chemotherapy can relieve symptoms in most cases and sometimes decreases tumor size. Single-modality therapies do not prolong survival. The effect of multimodal therapies overall and the contribution of each mode have not been established. Therapies under investigation include immunotherapy, gene therapy, photodynamic therapy, and hyperthermic intrapleural chemotherapy.
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