What Is Mesothelioma?
Mesothelioma is a benign (noncancerous) or malignant (cancerous) tumor affecting the mesothelium, which is a membrane that covers most of the body's internal organs. Most cases of mesothelioma begin in the pleura (lining around the lungs) or peritoneum (the lining around the abdomen).

Benign mesothelioma can also be called a fibroma, and cancerous mesothelioma is also known as malignant mesothelioma. A mesothelioma can further be named based on where it occurs. For example, malignant pleural mesothelioma is cancer that begins in the lining around the lungs.

Most people who develop malignant mesothelioma have worked on jobs where they inhaled asbestos particles. A benign mesothelioma does not appear to have any relationship to asbestos exposure.

Understanding the Mesothelium:
The mesothelium is a membrane that covers and protects most of the internal organs of the body. It is composed of two layers of cells: one layer immediately surrounds the organ; the other forms a sac around it. The mesothelium produces a lubricating fluid that is released between these layers, allowing moving organs (such as the beating heart and the expanding and contracting lungs) to glide easily against adjacent structures.

The mesothelium has different names, depending on its location in the body. The peritoneum is the mesothelial tissue that covers most of the organs in the abdominal cavity. The pleura is the membrane that surrounds the lungs and lines the wall of the chest cavity, while the pericardium covers and protects the heart. The mesothelial tissue surrounding the male internal reproductive organs is called the tunica vaginalis testis, and the tunica serosa uteri covers the internal reproductive organs in women.