Mesothelioma- the silent killer

The 3 major histological types of mesothelioma are

• sarcomatous,

• epithelial,

• mixed.
  

Pleural mesothelioma usually begins as discrete plaques and nodules that coalesce to produce a sheetlike neoplasm. Tumor growth usually begins at the lower part of the chest. Deposits of asbestos fibres deep in the base of the lungs may result in these fibres penetrating through into the pleural membranes where the fibre can then be carried to the pleural surface, then it may invade the diaphragm and encase the surface of the lung and interlobar fissures.

The tumor may also grow along drainage and thoracotomy tracts. As the disease progresses, it often extends into the pulmonary parenchyma, chest wall, and mediastinum. Pleural mesothelioma may extend into the

• esophagus,
• ribs,
• vertebra,
• brachial plexus,
• and superior vena cava.

This is the result in the penetration of the visceral pleura from where the fibre can then be carried to the pleural surface, thus leading to the development of malignant mesothelial plaques.

The processes leading to the development of peritoneal mesothelioma remain unresolved, although it has been proposed that asbestos fibres from the lung are transported to the abdomen and associated organs via the lymphatic system.

It is also believed that the development of peritoneal mesothelioma is proposed to have been result from asbestos fibres being coughed up and swallowed. Additionally, asbestos fibres may be deposited in the gut after ingestion of sputum contaminated with asbestos fibres.

In detail investigation, the development of mesothelioma in rats has been demonstrated following intra-pleural inoculation of phosphorylated chrysotile fibres. It shows that smaller particles may be more dangerous than the larger fibers.

It is believed that in humans, transport of fibres to the pleura is critical to the pathogenesis of mesothelioma. After the penetration there is evidence of recruitment of significant numbers of macrophages and other cells of the immune system to localised lesions of accumulated asbestos fibres. As the disease progressed, these lesions continued to attract and accumulate macrophages and cellular changes. Then eventually, within the lesion culminated in a morphologically malignant tumour.