Malignant mesothelioma is cancer that begins in the lining cells of certain parts of the body, especially in the lining of the chest or abdomen.
Cancer begins when the cells start to grow out of control. Cells in almost any part of the body can become cancer. To learn more about how cancers begin and spread, see What is cancer?
A layer of specialized cells called mesothelial cells lines the inside of the chest, abdomen, and space around the heart. These cells also cover the outer surface of most of your internal organs. The lining formed by these cells is called mesothelium.
The mesothelium protects your organs by making a special lubricating fluid that allows the organs to move against each other. For example, this fluid makes it easier for your lungs to move (expand and contract) inside your chest when you breathe. The mesothelium has different names in different parts of the body:
The pleura covers the lungs and space in the chest that contains the lungs.
The peritoneum covers the inside of the abdomen and many of the organs of the abdomen.
The pericardium covers the heart and creates the space that keeps the heart in the chest.
The tunica vaginalis covers the testes.
Mesothelial tumors can begin in any of these coatings. These tumors may be non-cancerous (benign) or cancerous (malignant).
A cancerous tumor of the mesothelium is called malignant mesothelioma, although it is often reduced to mesothelioma alone. Mesotheliomas can begin in 4 main areas of the body.
- Pleural mesotheliomas begin in the chest. Approximately 3 out of 4 mesotheliomas are pleural mesotheliomas.
- Peritoneal mesotheliomas begin in the abdomen. They constitute the majority of the remaining cases.
- Pericardial mesotheliomas begin in the envelope around the heart and are very rare.
- Mesotheliomas of the tunica vaginalis are very rare tumors that start in the covering layer of the testicles.
Malignant mesotheliomas can also be classified into 3 main types according to how the cancer cells are organized:
- About half of mesotheliomas are epithelioid. This type tends to have a better perspective (prognosis) than the other types.
- About 10% of mesotheliomas are sarcomatoid (fibrous).
- Mixed mesotheliomas (biphasic) have epithelioid and sarcomatoid areas. It constitutes the remaining 30% to 40% of mesotheliomas.
Benign tumors of the mesothelium
Benign (non-cancerous) tumors can also start in the mesothelium. These tumors are usually removed by surgery and, often, there is no need for additional treatment.
Localized fibrous tumor of the pleura
This type of benign tumor can form in the pleura that surrounds the lungs. It used to be called benign fibrous mesothelioma, but now doctors know that this tumor does not really start in the mesothelial cells. This disease is usually benign, but about 1 in 10 is cancerous. A similar condition that begins in the peritoneum is called solitary fibrous tumor of the peritoneum.
This benign tumor can develop in the mesothelium of certain reproductive organs. In men, it often begins in the epididymis (ducts that carry sperm cells out of the testicle). In women, this tumor can start in the fallopian tubes (tubes that carry the eggs from the ovaries to the uterus).