What is Malignant Mesothelioma of the Pleura

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Malignant mesothelioma of the pleura is a cancer which arises from the mesothelial cells found within the pleural membranes that cover the lungs. There are two pleurae: the visceral pleura, which covers the actual lung itself; and the parietal pleura, which covers the inside of the chest wall. The purpose of the pleura is to provide a smooth surface so that, as the chest expands, the lungs expand smoothly within the chest cavity. The pleural membranes normally secrete a small amount of fluid for lubrication. This allows the visceral pleura (lining the lungs) to glide over the parietal pleura (lining the inside of the chest cavity). Malignant mesothelioma develops from the mesothelial cells of the pleura.

Statistics on Malignant Mesothelioma of the Pleura

Malignant mesothelioma is relatively uncommon compared to other tumours. Australia has the highest incidence of mesothelioma in the world, at 40 cases per million people. Other industrialised countries which have mined and used asbestos, such as the United States, England, Canada and South Africa, have similar but slightly lower rates of disease.The incidence of mesothelioma increases with age, with most patients presenting between 50 and 80 years of age. This is because there is a latency period of as long as 50 years between exposure to asbestos and development of mesothelioma. Mesothelioma is far more common in men than in women, at a ratio of 4:1.

Risk Factors for Malignant Mesothelioma of the Pleura

The main predisposing factor is contact with asbestos. There are two major types of asbestos fibres: the long, thin ‘amphiboles’, and the feathery ‘chrysotile’ fibres.

Amphibole fibres include the known cancer-causing blue asbestos fibres, which have been definitively linked to the development of malignant mesothelioma. The long, thin shape of these fibres is thought to allow them to penetrate into the pleura, causing cycles of irritation, inflammation and thickening. Chrysotile fibres (including ‘white asbestos’) may also increase the risk of malignant mesothelioma, but the link is less clear.

People particularly at risk are those who have worked in the mining of asbestos, especially blue asbestos. Other at-risk jobs include ship builders, insulation workers, fitters, carpenters and electricians. Immediate family members of workers whose clothes have been contaminated with asbestos fibres are also at risk, even though the amount of exposure is very small.

Progression of Malignant Mesothelioma of the Pleura

Malignant mesothelioma grows in the pleural space surrounding the lungs. The tumour may eventually encase the entire lung. Local spread also occurs into nearby structures, such as the lung, chest wall, or the heart. In half of all cases, malignant mesothelioma spreads to other organs of the body, including the liver or, rarely, bone.

Symptoms of Malignant Mesothelioma of the Pleura

The most common presentation of malignant mesothelioma is with shortness of breath due to a pleural effusion (fluid accumulating between the lung and the chest wall, which has the effect of squashing the lung). Chest pain may also occur. Later in the disease, patients may experience weight or appetite lossfatigue, fever, night sweats or anaemia.

How is Malignant Mesothelioma of the Pleura Diagnosed?

full blood picture may show anaemia and a high platelet count. Imaging tests such as a chest x-ray (see the example below), CT, MRI or PET scan can be used to assess the extent of local tumour invasion and whether the tumour has spread.

Malignant mesothelioma: x-ray

To confirm a diagnosis of malignant mesothelioma, cancer cells must be seen under the microscope. These cells can be obtained a number of ways:

  • Diagnostic thoracentesis allows drainage of any pleural effusion which has developed. The cells in the effusion can then be analysed. Cancer cells are seen in pleural effusions in 33-84% of cases of malignant mesothelioma.
  • CT-guided core biopsy through the chest wall is even better at detecting malignant (cancerous) cells.

Prognosis of Malignant Mesothelioma of the Pleura

Malignant mesothelioma is only very rarely curable, either by surgery, radiotherapy or chemotherapy. The median survival from time of diagnosis is only one year. Outcomes are worse for male patients, and for patients with extensive disease at diagnosis.

How is Malignant Mesothelioma of the Pleura Treated?

Malignant mesothelioma is usually incurable at presentation. Treatment is therefore aimed at controlling symptoms and prolonging survival, rather than trying to remove the tumour.

Surgery

It is very rarely possible to surgically remove a malignant mesothelioma, because the tumour spreads widely throughout the pleura and invades nearby organs. Instead, palliative surgery may occasionally be used to try to control symptoms, particularly pleural effusion.

Radiotherapy

It is difficult to treat malignant mesothelioma with radiotherapy because the tumour involves such a large area of the chest wall. However, there are two situations in which radiotherapy may be used.

Radiotherapy may be used to treat sites where biopsies have been taken or chest drains inserted. These areas, where a tube has been passed through the chest wall into the pleural space, often become ‘seeded’ with the mesothelioma tumour. This then presents as a growing lump a number of months later. If radiotherapy to the area is given soon after diagnosis, any tumour cells which have ‘seeded’ the area can be destroyed.

Radiotherapy may also be used to treat pain in the chest wall due to spread of the tumour.

Chemotherapy

Until recently, chemotherapy was not thought to be useful in treating malignant mesothelioma. However, recent studies have shown that treatment with the drugs cisplatin and pemetrexed (Alimta) may reduce tumour size, increase patient survival by several months, and improve quality of life.

Research is continuing for a variety of other asbestosis treatments such as vaccine therapy and other immune therapies. It is hoped that some of the newer biological agents may also have some effect.

 

Drugs used to treat this disease:

Malignant Mesothelioma of the Pleura References

  1. Braunwald, Fauci, Kasper, Hauser, Longo, Jameson. Harrison’s Principles of Internal Medicine. 16th edition. McGraw-Hill. 2005.
  2. Cotran, Kumar, Collins. Robbins Pathologic Basis of Disease. 6th edition. WB Saunders Company. 1999.
  3. Hawley R, Monk A. Malignant mesothelioma: Current practice and research directions. Collegian. 2004; 11(2): 22-6.
  4. Ismail-Khan R, et al. Malignant pleural mesothelioma: A comprehensive review. Cancer Control. 2006; 13(4): 255-63.
  5. Robinson BWS, Lake RA. Advances in malignant mesothelioma. New England Journal of Medicine. 2005; 353(15): 1591-603.
  6. Talley NJ, O’Connor S. Clinical Examination. 4th edition. MacLennan & Petty. 2001.
  7. Zucali PA, Giaccone G. Biology and management of malignant pleural mesothelioma. European Journal of Cancer. 2006; 42(16): 2706-14.