Mesothelioma is a rare type of cancer that develops in the mesothelial cells lining various organs and body cavities. The mesotelium (composed of mesothelial cells) is the membrane that lines three body cavities, and depending on the cavity that is lined is assigned a specific name: the thoracic cavity (pleura), abdominal cavity (peritoneum), and bag the heart (pericardium).

The mesothelium that covers the internal organs is called visceral mesothelium, while the coating on the body wall is called the parietal mesothelium.

The mesotelium tissue also surrounds the male internal reproductive organs and covers the internal reproductive organs in women.

Mesothelioma is an aggressive cancer of the mesothelium, in which cells of the mesothelium become abnormal and divide uncontrollably. They can invade and damage tissues and organs. Most cases of mesothelioma rises in the chest cavity (pleura) or the abdominal cavity (peritoneum)

Approximately 2000-3000 cases of mesothelioma are diagnosed each year in the United States, covering about 3 percent of all cancer diagnosis. This cancer occurs four times more common in men than in women. Any form of mesothelioma is fatal, with the exception of benign mesothelioma. The prognosis for mesothelioma is almost always poor and most studies report a median survival of less than a year, but the outlook really depends on how early the diagnosis is made and if it aggressively.