What is Mesothelioma?

Mesothelioma (cancer of the mesothelium) is a disease in which cells of the mesothelium become abnormal and divide without control or order. Mesothelioma is a cancer of the linings of the lungs, chest, abdomen, and the organs contained in those areas, rather than a cancer that forms in the lungs. They can invade and damage nearby tissues and organs. Cancer cells can also metastasize (spread) from their original site to other parts of the body.

Mesothelioma is most frequently caused by exposure to asbestos. Asbestos is a group of naturally occurring minerals. Asbestos releases strong, microscopic fibers that may injure the protective linings surrounding the body's organs. Most cases of mesothelioma begin in the pleura or peritoneum.

Malignant mesothelioma is an uncommon, but no longer rare, cancer that is difficult to diagnose and poorly responsive to therapy. Malignant mesothelioma is the most serious of all asbestos-related diseases. Thousands of Americans die each year from asbestos related disease including mesothelioma cancer.

A layer of specialized cells called mesothelial cells lines the chest cavity, abdominal cavity, and the cavity around the heart. These cells also cover the outer surface of most internal organs. The tissue formed by these cells is called mesothelium. There are three main types of malignant mesothelioma: epithelial, sarcomatoid and mixed. The epithelial type is the most common.

The mesothelium helps protect the organs by producing a special lubricating fluid that allows organs to move around. For example, this fluid makes it easier for the lungs to move inside the chest during breathing. The mesothelium of the chest is called the pleura and the mesothelium of the abdomen is known as the peritoneum. The mesothelium of the pericardial cavity (the "sac-like" space around the heart) is called the pericardium.

Tumors of the mesothelium can be benign (noncancerous) or malignant (cancerous). A malignant tumor of the mesothelium is called a malignant mesothelioma. Because most mesothelial tumors are cancerous, malignant mesothelioma is often simply called mesothelioma.

Mesothelioma was recognized as a tumor of the pleura, peritoneum and pericardium in the late 1700's. However it was not until much later, in 1960, that this particular type of tumor was described in more detail and even more importantly, its association with asbestos exposure was recognized. The first report linking mesothelioma to asbestos exposure was written by J.C.Wagner, and described 32 cases of workers in the "Asbestos Hills" in South Africa. Since then, the relationship between mesothelioma and asbestos exposure has been confirmed in studies around the world. Once it develops, this type of cancer will continue to grow and spread until it is treated.

About three-fourths of malignant mesothelioma occurrences start in the chest cavity and is known as pleural mesothelioma. Another 10% to 20% begin in the abdomen and is called peritoneal mesothelioma. Pericardial mesothelioma, starting in the cavity around the heart, is very rare. The covering layer of the testicles is actually an out pouching of peritoneum into the scrotum. Mesothelioma that affects this covering of the testicles is quite rare.

About 90 percent of people who are diagnosed with malignant mesothelioma have chest pain or shortness of breath as the first symptoms of the disease. Chest pain is caused mainly by the cancer itself, which irritates nerve cells in nearby tissues. Less severe chest discomfort and shortness of breath generally are caused by a collection of fluid between the two layers of the pleura in the chest, not by the cancer itself. This collection of fluid is called a pleural effusion. People with mesothelioma that develops in the abdominal lining can have abdominal pain and swelling caused by an accumulation of fluid in the abdominal cavity. Other possible symptoms include cough, fatigue and unexplained weight loss.

Mesothelioma is not caused by smoking, as lung cancer so often is. Instead, mesothelioma is tied almost exclusively to the mineral asbestos. Of the 2,000 new cases of mesothelioma reported in the United States each year, 70 to 80 percent can be traced to tiny, airborne shards of asbestos, which in the past was used in the production of construction materials ranging from cement to shingles to siding, and was extensively used as insulation.

Mesothelioma also is not a disease of the past. Although protections against occupational asbestos exposure have been in place since the 1970s, asbestos-related cancers such as mesothelioma can take 30 to 50 years to show up, according to the Mesothelioma Applied Research Foundation.

There are several misconceptions about mesothelioma. For one thing, it is not lung cancer. It is a cancer of the two-layered membrane that covers and protects most of the body’s organs. That membrane, the mesothelium, is also called pericardium where it covers the heart, peritoneum where it surrounds most of the other abdominal organs, and pleura where it envelops the lungs, which is also where it most often turns cancerous.

The mesothelium of the chest is called the pleura.

The mesothelium of the abdomen is known as the peritoneum.

The mesothelium of the pericardial cavity ("sac-like" space around the heart) is called the pericardium. About 50 to 70 percent of its occurrences are the epithelioid type: This type has the best forecast (outlook for survival).