Mesothelioma

What is mesothelioma?

Mesothelioma is a rare cancer with a terminal prognosis caused by asbestos exposure. Accounting for fewer than 1% of all cancers, it affects the mesothelial cells, which make up the mesothelium, the membrane that lines the outer surface of most organs. Mesothelioma is caused when asbestos fibres make their way into the mesothelium. The onset of disease may present many years after the initial exposure ranging from 10-50 years.

Australia has one of the highest incidences of mesothelioma in the world. According to the Australian Mesothelioma Registry, each year over 700 Australians are diagnosed with pleural mesothelioma. Men are over three times more likely than women to be diagnosed with pleural mesothelioma. This is probably because many cases have been caused by exposure to asbestos at work. Western Australia has the most cases per population due to past asbestos mining. Pleural mesothelioma is more common in people over the age of 70, but can sometimes occur in younger people.

Currently, there is no cure for mesothelioma. Certain treatments may extend life expectancy and help achieve long-term remission dependant on the stage of diagnosis, type of cancer and patient health, however, due to the aggressive nature of mesothelioma and often late diagnosis, the mesothelioma survival rates are very low.  This is what ADDRI is working hard to address.

Types of mesothelioma

There are two main types of mesothelioma, which are classified according to the area affected.

• Pleural – this forms in the covering of the lungs. Pleural mesothelioma is the most common type, accounting for about 90% of all mesotheliomas. This type of mesothelioma is called malignant pleural mesothelioma (MPM). We refer to it as pleural mesothelioma or, simply, mesothelioma.
• Peritoneal – this develops in the lining of the abdomen. It accounts for about 10% of cases and is called malignant peritoneal mesothelioma.

Rarely, mesothelioma occurs in the pericardium (the membrane around the heart) or the tunica vaginalis (the membrane around the testicles). Although pleural mesothelioma develops in the chest and involves the lining of the lungs, it is not lung cancer and is diagnosed and treated differently.

The pleura

The chest wall and lungs are covered by two layers of a thin sheet of tissue called the pleura.

• The inner layer (visceral pleura) – lines the lungs.
• The outer layer (parietal pleura) – lines the chest wall and the diaphragm.

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 (inhalation). When excess fluid collects between the two layers, this is known as a pleural effusion.

Cell types of mesothelioma

Mesothelioma is also grouped according to how the cells look under a microscope. There are three main types:

• Epithelioid – cells look similar to normal mesothelial cells. This is the most common type, making up about 60% of cases.
• Sarcomatoid – cells have changed and look like cells from fibrous tissue. Accounts for about 15% of cases.
• Mixed or biphasic – has epithelioid and sarcomatoid cells. These make up about 25% of all cases.
  Mesotheliomas can differ in the way they grow. Some form a mass; others grow along the pleura forming a thick covering on the lungs.

What causes pleural mesothelioma

Exposure to asbestos is generally the only known cause of mesothelioma. Sometimes mesothelioma is 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. People most likely to have been exposed to asbestos at work include asbestos miners and millers, transport workers (especially waterside workers), laggers and insulators, builders, plumbers and electricians, mechanics, and asbestos cement manufacturing workers. People who haven’t worked directly with asbestos, but have been exposed to it, can also develop mesothelioma. This can include people washing or cleaning work clothes with asbestos fibres on them or people renovating homes. It can take many years after being exposed to asbestos for mesothelioma to develop. This is called the latency period or latent interval, and is usually between 20 and 60 years.

Symptoms

The earliest signs of pleural mesothelioma are often vague and similar to other conditions or diseases. If you are concerned, especially if you think you’ve been exposed to asbestos, see your general practitioner (GP).

• Shortness of breath (breathlessness) – Most people with pleural mesothelioma experience breathlessness. You may feel like you can’t catch your breath no matter what you do. It usually feels worse with activity or when you are lying down. In early mesothelioma, breathlessness is caused by a build-up of fluid in the chest (pleural effusion).
• Pain – This can be a sharp pain in the chest, which affects your breathing, or a dull pain in the shoulder and upper arm. The pain might not improve with pain relievers.
• Other general symptoms – Less commonly, people notice loss of appetite with weight loss, a persistent cough, or a change in their coughing pattern. Some people also experience heavy sweating, especially at night.

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