What is mesothelioma?
Mesothelioma is a type of cancer that starts from mesothelial cells. These cells line the outer surface of most of the body’s internal organs, forming a protective membrane called the mesothelium.
Some mesotheliomas form a mass (tumour), while others grow along the mesothelium and form a thick covering. In later stages, mesothelioma may spread (metastasise) to other parts of the body.
The mesothelium that covers the lungs is called the pleura. Mesothelioma that develops in the pleura is known as malignant pleural mesothelioma or, simply, pleural mesothelioma. It accounts for more than 90% of all mesotheliomas. Although pleural mesothelioma involves the lining of the lungs, it is not lung cancer and is diagnosed and treated differently.
There are two layers in the pleura. The inner layer lines the surface of the lungs and is called the visceral pleura. The outer layer lines the chest wall and the diaphragm, and is called the parietal pleura.
Between the two layers is the pleural cavity (also called the pleural space), which normally contains a small amount of fluid. This fluid allows the two layers of pleura to slide over each other so the lungs move smoothly against the chest wall when you breathe.
When mesothelioma develops in the pleura, the delicate layers of the pleura thicken and may press on the lung, preventing it from expanding when breathing in (inhaling). Excess fluid often collects between the two layers – this is called a pleural effusion.
The mesothelium that lines the walls and organs of the abdomen and pelvis is called the peritoneum. Mesothelioma that develops in the peritoneum is known as malignant peritoneal mesothelioma or, simply, peritoneal mesothelioma. It accounts for less than 10% of all mesotheliomas.
The peritoneum has two layers. The inner layer lines the surface of organs such as the bowel, liver and ovaries and is called the visceral peritoneum. The outer layer lines the walls of the
abdomen and pelvis, and is called the parietal peritoneum. Between the two layers is the peritoneal cavity, which normally contains a small amount of fluid. This fluid allows the two layers to slide over each other as you move around. In people with peritoneal mesothelioma, excess fluid often collects between the two layers – this is known as ascites or peritoneal effusion.
What causes mesothelioma?
A: Exposure to asbestos is the main cause of mesothelioma. Very rarely, mesothelioma has been linked with previous radiotherapy to the chest. Asbestos is the name of a group of naturally occurring minerals that are resistant to high temperatures and humidity.
It was used in many building products in Australia from the 1940s until 1987. Since 2004, Australia has had a ban on asbestos being sold, reused and/or imported. It is still present
in many older buildings, so special precautions must be taken when renovating or demolishing. It has also been found in some recently imported products despite the ban.
People most likely to have been exposed to asbestos at work include asbestos miners and millers, asbestos cement manufacturing workers, laggers and insulators, builders, plumbers and electricians, automotive industry workers, mechanics, transport workers (especially waterside workers), and textile workers. People who haven’t worked directly with asbestos but have been exposed to it can also develop mesothelioma. These can include people cleaning work clothes with asbestos fibres on them or people disturbing asbestos during home renovations or maintenance.
It can take many years for mesothelioma to develop after a person is exposed to asbestos. This is called the latency period or interval – it is usually between 20 and 60 years (most commonly around 40 years) after exposure.