Mesothelioma is a type of cancer.  It is a cancer of mesothelial cells.  These cells cover the outer surface of most of our internal body organs, forming a lining that is sometimes called the mesothelium.  So this is where this type of cancer gets its name. 

 Mesothelioma cancer can develop in the tissues covering the
  lungs & abdomen

The tissues lining (or covering) the lungs are called the pleura.  There are two pleura.  These can be called pleural membranes.  The gap between them is called the pleural space.  The pleura are fibrous sheets.  They help to protect the lungs.  They produce a lubricating fluid that fills the gap between the two pleura.  This helps the lungs to move smoothly in the chest when they are inflating and deflating as we breathe.

Mesothelioma is most often diagnosed in the pleura.  This is known as pleural mesothelioma. Because it is so close, pleural mesothelioma can also affect the sheet of tissue covering the heart - the pericardium.  Doctors call the pericardium the lining, although it is on the outside of the heart.  It protects the heart and allows it to move smoothly within the sac that surrounds it.  So it does much the same job for the heart as the pleura do for the lungs.

The tissue lining the abdomen is called the peritoneum.  It helps to protect the contents of the abdomen.  It also produces a lubricating fluid.  This helps the organs to move smoothly inside the abdomen as we move around.

Mesothelioma of the tissues lining the abdominal cavity in known as peritoneal mesothelioma.  It is much less common than pleural mesothelioma.

It is unusual for mesothelioma to spread to other parts of the body.  But if it does, it does not usually cause troublesome symptoms.

Benign mesothelioma

There is a form of non cancerous (benign) mesothelioma that can develop in the lining of the lungs, or in the lining of the reproductive organs.  It can occur in either men or women.  These non cancerous tumours are very rare.