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CANCER WELLNESS

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BENIGN LUNG TUMOURS

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Asbestos: Related Diseases

The differences between mesothelioma and asbestosis

What Causes Mesothelioma Cancer

How To Reduce Mesothelioma Cancer Risk

Asbestos is a mixture of silicates of iron, magnesium, nickel, cadmium and aluminium, and has the unique property of occurring naturally as a fibre. It is remarkably resistant to heat, acid and alkali, and has been widely used for roofing, insulation and fireproofing. Asbestos has been mined in southern Africa, Canada, Australia and eastern Europe. Several different types of asbestos are recognized: about 90% of asbestos is chrysotile, 6% crocidolite and 4% amosite. Chrysotile or white asbestos is the softest asbestos fibre. Each fibre is often as long as 2 cm but only a few microns thick. It is less fibrogenic than crocidolite. Crocidolite (blue asbestos) is particularly resistant to chemical destruction and exists in straight fibres up to 50 mm in length and 1-2μm in width. Crocidolite is the most likely type of asbestos to produce asbestosis and mesothelioma. This may be due to the fact that it is readily trapped in the lung. Its long, thin shape means that it can be inhaled, but subsequent rotation against the long axis of the smaller airways, particularly in turbulent airflow during expiration, causes the fibres to impact. Crocidolite is also particularly resistant to macrophage and neutrophil enzymatic destruction.

Exposure to asbestos occurred particularly in shipbuilding yards and in power stations, but its ubiquitous use meant that low levels of exposure were common. Up to 50% of urban dwellers have been found to have asbestos bodies (asbestos fibre covered in protein secretions) in their lungs at post-mortem. Regulations in the UK prohibit the use of crocidolite and severely restrict the use of chrysotile. Careful dust control measures are enforced, which should eventually abolish the problem. Workers continue to be exposed to blue asbestos in the course of demolition or in the replacement of insulation, and it should be remembered that there is a considerable time lag between exposure and development of disease, particularly mesothelioma (20-40 years).

A synergistic relationship exists between asbestosis and cigarette smoking and the development of bronchial carcinoma, usually adenocarcinoma; the risk is multiplied fivefold above the risk attributable to smoking. The risk of lung cancer is also increased in non-smokers, especially in those who have parenchymal asbestosis but also in those with pleural plaques without parenchymal fibrosis.

The diseases caused by asbestos are summarized in the table above Bilateral diffuse pleural thickening, asbestosis, mesothelioma and asbestos-related carcinoma of the bronchus are all eligible for industrial injuries benefit in the UK, but account for only one-quarter of the number of cases of compensation compared with coal-worker's pneumoconiosis.

Asbestosis is defined as fibrosis of the lungs caused by asbestos dust, which may or may not be associated with fibrosis of the parietal or visceral layers of the pleura. It is a progressive disease characterized by breathlessness and accompanied by finger clubbing and bilateral basal end-inspiratory crackles. Fibrosis, not detectable on chest X-ray, may be revealed on CT scan. No treatment is known to alter the progress of the disease, though corticosteroids are often prescribed.

Mesothelioma

The number of cases of mesothelioma has increased progressively since the mid-1980s and has now reached over 1000 cases per year. Pleural effusions are the most common presentation of mesothelioma, typically with persistent chest wall pain, which should raise the index of suspicion even if the initial pleural fluid or biopsy samples are non-diagnostic. Often a video-assisted thoracoscopic lung biopsy is needed to obtain sufficient tissue for diagnosis. In the event of a positive pleural biopsy diagnosis, local radiotherapy should be given to prevent the seeding of mesothelioma cells down the needle track. No treatment influences the universally fatal outcome.