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 membrane called the mesothelium. The membrane that covers the lungs is the pleura.
- Types of mesothelioma
- How common is pleural mesothelioma?
- What causes pleural mesothelioma?
- What will it mean for me?
- The lungs
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). In this book 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.
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.
How common is pleural mesothelioma?
Australia has one of the highest rates of mesothelioma in the world. According to the Australian Mesothelioma Registry, each year close to 600 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.
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.
People who develop mesothelioma due to asbestos exposure may be able to claim compensation. It’s important to get legal advice from an experienced lawyer as soon as possible after diagnosis.
What will it mean for me?
When your doctor first suggests that you may have pleural mesothelioma, you and your family will be understandably shocked. It’s common to have many questions and concerns about what the diagnosis will mean for you.
To understand what is happening, it may help to break down the process into a series of steps. The diagram opposite is a guide to the main steps. Mesothelioma is different for everyone and you may not go through each step in the order shown. You can use the diagram to see what stage you are at and read the chapter relevant to you.
The diagnosis stage is represented as a central pathway leading to active treatment. This will involve making treatment decisions about the best care for you. During these periods, your health care team will also focus on treating symptoms and improving your quality of life.
The blue arrows represent the quality of life experienced while living with pleural mesothelioma. Depending on the impact of pleural mesothelioma on your health, you may experience periods of relatively good health when symptoms are under control or less active. These alternate with periods when symptoms are less controlled and the intensity of treatment needs to be increased to improve quality of life.
The lungs are the main organs for breathing and are part of the respiratory system. The respiratory system also includes the nose, mouth, windpipe (trachea) and airways to each lung. These consist of large airways (bronchi) and smaller airways (bronchioles).
The lungs look like two large, spongy cones. Each lung is made up of sections called lobes – the left lung has two lobes and the right lung has three. The lungs rest on the diaphragm, which is a wide, thin muscle that helps with breathing.
The role of 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.