Mesothelioma is a form of cancer in which malignant cells are found in the mesothelium. The mesothelium is a membrane that covers and protects most of the internal organs of the body. It is made of two layers of cells. One layer surrounds the organ and the other forms a sac around it. The mesothelium produces a lubricating fluid that is released between these layers, allowing moving organs to glide easily against adjacent structures.

 

With mesothelioma the cells of the mesothelium become abnormal and divide without control or order. They invade and damage nearby tissues and organs. Cancer cells can also spread from their original site to other parts of the body. Most cases of mesothelioma begin in the pleura or peritoneum. About 2,000 new cases of mesothelioma are diagnosed in the United States each year. Working with asbestos is the major risk factor for mesothelioma. A history of asbestos exposure at work is reported in about 75 percent of all cases. Asbestos is a group of minerals that occur as masses of strong flexible fibers are separated into thin threads and woven.