Occupational lung diseases- Pleural mesothelioma
Mesothelioma is a tumour of the mesothelial lining of the pleural, pericardial and peritoneal cavities.
Pleural mesothelioma is currently uncommon, with an incidence of 8 per 100 000 per year in the United Kingdom. However, asbestos use was widespread in Europe until the 1980s and, due to an approximate 40-year latent period between exposure and presentation, it has been projected that the peak incidence is likely to occur around 2020, individuals born between 1945 and 1950 being at greatest risk. Pleural mesothelioma is more common in men than in women.
Asbestos is the primary aetiological exposure that results in the development of mesothelioma. Any evidence of exposure is relevant, as no threshold exposure exists for the risk of mesothelioma. The four histopathological subtypes are epithelioid, sarcomatoid, biphasic (epithelioid and sarcomatoid) and desmoplastic.
The presentation of malignant pleural mesothelioma is often insidious and non-specific. Progressive dyspnoea and/or dull and diffuse chest pain are the two most common symptoms. The pain may radiate to shoulder, arm, chest wall or abdomen and may occasionally be pleuritic. Systemic symptoms of malignancy include anorexia, weight loss and pyrexia. A detailed occupational history is the key to determine any evidence of asbestos exposure.
On examination, clubbing may be present. Chest examination may reveal features exactly like those of a pleural effusion . In advanced disease, cachexia, chest wall mass, hepatomegaly or ascites may be present.
The plain film appearances may be similar to a pleural effusion, but the abnormal area may be composed in part or entirely of tumour, or isolated pleural thickening. Other evidence of asbestos exposure may be present such as pleural plaques (nodular or irregular pleural shadowing) that may extend to the mediastinal aspect, pleural calcifications or pulmonary fibrosis-asbestosis.
A CT scan may have been part of the diagnostic workup for a pleural effusion of unknown cause. Features of mesothelioma are the presence of discrete pleural masses. Multiloculated effusions may be present and a think pleural rind in more established disease. In addition, CT-guided biopsy of a pleural nodule can provide valuable tissue samples for histopathological analysis. The CT scan is also an excellent staging investigation that can assess the extent of local invasion and regional lymphadenopathy.
Pleural aspiration cytology and percutaneous pleural biopsies have poor sensitivity, therefore a negative test cannot confidently rule out disease. However, confirmatory histopathological diagnosis is essential, and if necessary a surgical biopsy should be undertaken.
As with all other tumours, confirmatory histopathological diagnosis and staging are fundamental to the management of patients with malignant pleural mesothelioma.
Patients should be informed that the prognosis is poor despite a current trimodality approach of surgery (where appropriate), radiotherapy and chemotherapy. Financial compensation is usually provided for industry-related mesothelioma, and advice on how to make a claim is important.
The efficacy of radical surgery has not been evaluated in the setting of a randomized trial. Surgery for stage I/II disease should be confined to patients with a favourable histological subtype (epithelioid) and centres with specialist expertise in pleural mesothelioma. Extrapleural pneumonectomy (resection of the lung, viscera, parietal pleura, pericardium, and ipsilateral diaphragm) has a mortality rate of approximately 30% in inexperienced and less than 5% in experienced centres. Video-assisted thoracoscopic (VATS) decortication and pleurodesis is also an option for the palliative management of symptomatic pleural effusions, although it remains controversial as a definitive management strategy.
Pleural mesothelioma is a relatively radioresistant disease. The role of radiotherapy is confined to palliation (of chest pain), prophylactic (along needle aspiration, biopsy and surgical incision, and chest drain sites) and postoperative adjuvant therapy that may reduce recurrence in selected patients.
Pleural mesothelioma is also a relatively chemoresistant disease. Initial single agent chemotherapy regimens have failed to produce response rates above 30%. Pemetrexed, a potent inhibitor of proteins required for DNA synthesis, prolongs median survival from 9 to 12 months. Gemcitabine in combination with cisplatin has also resulted in objective response rates and improved quality of life.
The results of biological therapy with imatinib (platelet derived growth factor inhibitor) and gefitinib (epidermal growth factor receptor blocker) have not yet yielded convincing responses.
The prognosis of pleural mesothelioma is related to stage. In general, the prognosis is very poor with a median survival of less than one year.
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