Mesothelioma is a cancer that most commonly starts in the layers of tissue that cover each lung (the pleura). Rarely it starts in the layer of tissue in the abdomen which surrounds the digestive system organs (the peritoneum).
How common it is
In the UK around 2,700 people are diagnosed with mesothelioma each year. It is quite a rare cancer, but it is becoming more common.
Mesothelioma in the chest (pleural mesothelioma) is much more common than mesothelioma in the abdomen (peritoneal mesothelioma).
Who gets it
Mesothelioma is more common in men than women. This is probably because it is often caused by exposure to asbestos at work.
It is more common in older people. In the UK, on average each year, around 50 out of 100 (around 50%) of the cases were diagnosed in people aged 75 and over.
Where it starts
Mesothelioma starts in the types of cells that cover the outer surface of most of our internal body organs (mesothelial cells). These cells form a lining called the mesothelium.
Around 9 out of 10 (90%) mesotheliomas are in the chest. This is called pleural mesothelioma.
3 out of 100 (3%) mesotheliomas are in the tummy (abdomen). This is called peritoneal mesothelioma.
The lungs and pleura
Pleural mesothelioma starts in the two sheets of tissue that cover your lungs (called pleura or pleural membranes). The gap between the pleura is called the pleural space.
These sheets help to protect your lungs. They also make a fluid that helps them slide over each other when your lungs expand and deflate as you breathe. The gap between these sheets is called the pleural space.
The sheet of tissue covering the heart (the pericardium) is very close to the pleura. So in some people pleural mesothelioma may also spread into the pericardium. The diagram below shows the pleura thickening due to mesothelioma.
The abdomen and peritoneum
The sheet of tissue covering the organs of your tummy (abdomen) is called the peritoneum. It helps to protect the contents of your tummy and keep them in place. It also makes a lubricating fluid that helps the organs inside move smoothly against each other as you move around.
Mesothelioma of the tissues lining your abdominal cavity is called peritoneal mesothelioma. It does not usually spread to other parts of the body.
Very rarely, a non cancerous (benign) type of mesothelioma can develop in the lining of your lungs or the lining of your reproductive organs. This can happen in men and women. These tumours are so rare that we don't cover them here.