What is mesothelioma?

Mesothelioma is a cancer that usually starts in the layers of tissue that cover each lung (the pleura). This is called pleural mesothelioma. 

More rarely it can start in the peritoneum. The peritoneum is the layer of tissue that covers the organs in your tummy (abdomen). This is called peritoneal mesothelioma.  

How common is mesothelioma?

In the UK around 2,700 people are diagnosed with mesothelioma each year. It is quite a rare cancer.

Mesothelioma in the chest (pleural mesothelioma) is much more common than mesothelioma in the abdomen (peritoneal mesothelioma).

Who gets mesothelioma?

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, 55 out of 100 (55%) people diagnosed are aged 75 and over.

Where does mesothelioma start?

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. In the UK:

• 95 out of 100 mesotheliomas (95%) are in the chest. This is called pleural mesothelioma.
• 4 out of 100 mesotheliomas (4%) are in the tummy (abdomen). This is called peritoneal mesothelioma. 
• less than 1 out of 100 mesotheliomas (less than 1%) are in the lining of the heart (pericardium). This is very rare.  

For a small number of mesotheliomas, the site where they started is not known or registered.

The lungs and pleura

Pleural mesothelioma starts in the two sheets of tissue that cover your lungs, called the 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 sheet of tissue covering the heart, called 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 abdomen 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 abdomen is called peritoneal mesothelioma. It does not usually spread to other parts of the body.

Benign mesothelioma

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.