Malignant mesothelioma is cancer that starts in the cells that line certain parts of the body, especially the chest, belly (abdomen), and heart. The lining formed by these cells is called mesothelium. These cells protect organs by making a special fluid that allows the organs to move. For instance, this fluid makes it easier for the lungs to move during breathing.

Tumors of the mesothelium can be benign or they can be cancerous. A cancerous tumor of the mesothelium is called a malignant mesothelioma, but this is often shortened to just mesothelioma. The information that follows covers only those tumors that are cancer.

Main types of mesothelioma

There are 3 main types of mesotheliomas based on how the cells look under a microscope.

• epithelioid: This is the most common type. It tends to have a better outlook (prognosis) than the other types.

• sarcomatoid (fibrous): About 1 or 2 out of 10 mesotheliomas are of this type.

• mixed (biphasic): This type has features of the 2 types above. About 3 or 4 out of 10 mesotheliomas are the mixed type.

About 3 out of 4 mesotheliomas start in the chest cavity. These are called pleural mesotheliomas. Another 10%-20% begin in the abdomen (belly). These are called peritoneal mesotheliomas. Those starting around the heart are very rare. This cancer can also start in the tissue around the testicles, but this is also very rare.

Last Medical Review: 04/01/2009
Last Revised: 04/01/2009