Malignant tumours of the mesothelium are cancerous growths that have the potential to spread (metastasize) to other parts of the body. Malignant mesothelioma is an uncommon cancer that starts in the mesothelial cells. Mesothelial cells form a lining called the mesothelium, which covers the outer surface of most internal organs.
The most common places for mesothelioma to develop are the pleura (the membrane that covers the lungs and lines the chest), followed by the peritoneum (the membrane that covers the abdominal organs and lines the abdomen).
Most people who develop mesothelioma have a history of exposure to asbestos.
Mesothelioma can be grouped into 3 main subtypes based on how the cells look under the microscope (histology). The 3 subtypes of mesothelioma are:
Although the different subtypes of mesothelioma are generally treated the same, knowing the subtype helps doctors predict prognosis and how the disease will respond to treatment.
Mesothelioma most often develops in the pleura and accounts for about 70%–80% of all cases of malignant mesothelioma. Mesothelioma causes thickening of the pleura and most people develop a pleural effusion (abnormal buildup of fluid in the pleural space).
Mesothelioma typically grows along the pleura and extends to the muscles, ribs and diaphragm. Pleural mesothelioma does not usually spread beyond the chest until late in the course of the disease. Spread to the lymph nodes is more likely to occur with pleural mesothelioma than with peritoneal mesothelioma.
It can be difficult to tell pleural mesothelioma from other lung conditions, such as lung cancer.
Peritoneal mesothelioma is the second most common type of mesothelioma. It accounts for up to 25% of all cases of malignant mesothelioma. Most people develop ascites or peritoneal effusion (abnormal buildup of fluid in the abdomen).
Peritoneal mesothelioma often remains confined to the abdomen. However it is usually widespread throughout the peritoneal cavity. Peritoneal mesothelioma can spread to the pleural cavity. Spread (metastasis) to distant sites is not common with peritoneal mesothelioma and it does not usually spread to lymph nodes.
Very rarely, mesothelioma can develop in the pericardium and the testicle.
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