Mesotheliomas can start in four main areas in the body: 

• the chest – the cancer starts in the mesothelium that lines the lungs (the pleura); this makes up about three-quarters of mesotheliomas 
• the abdomen – the cancer starts in the mesothelium that lines the abdomen (the peritoneum); this makes up most of the remaining cases of mesothelioma 
• the heart – the cancer starts in the mesothelium that surrounds the heart (the pericardium); this is very rare 
• the testes – the cancer starts in the mesothelium that covers the testicles; this is also very rare. 

This section of the website relates mainly to pleural mesothelioma (in the lining of the lungs). 

Mesothelioma can also be divided into types based on how the cancer cells are arranged: 

• epithelioid 
• sarcomatoid (fibrous)  
• mixed (biphasic)