Mesothelioma is a type of cancer that starts from mesothelial cells. These cells line the outer surface of most of the body’s internal organs, forming a protective membrane called the mesothelium.
Some mesotheliomas form a mass (tumour), while others grow along the mesothelium and form a thick covering. In later stages, mesothelioma may spread (metastasise) to other parts of the body.
The mesothelium that covers the lungs is called the pleura. Mesothelioma that develops in the pleura is known as malignant pleural mesothelioma or, simply, pleural mesothelioma. It accounts for more than 90% of all mesotheliomas.
Although pleural mesothelioma involves the lining of the lungs, it is not lung cancer and is diagnosed and treated differently.