Mesothelioma: The Basics

What is mesothelial tissue?

The mesothelium is a protective sac that covers and protects most internal organs in the body. It is composed of two layers, one layer covers the organ and the second layer forms a sac around it. The mesothelium produces a lubricating fluid that is released between these layers, allowing moving organs (such as the lungs) to move easily. The area between the two layers is often called the pleural space. Mesothelial tissue is found lining the abdominal cavity organs, lungs, testes and heart.

What is mesothelioma?

Mesothelioma occurs when the mesothelial cells grow out of control. These cells also lose the ability to stop producing the lubricating fluid when there is enough. This results in the unwanted encasement of organs within a thick rind of tumor tissue and excess fluid build up, ultimately causing symptoms. These cells can grow and invade other organs, or spread to other areas of the body. When the cells spread to other areas of the body, it is called metastasis.

The majority of mesotheliomas are found in the lining of the lung (65-70%). About 20-30% percent of cases are found in the abdominal cavity lining, and even more rarely, mesothelioma is found in the lining of the heart (1-2%) or testicles.

Am I at risk for mesothelioma?

Mesothelioma is a rare cancer, with approximately 2,000 cases diagnosed each year in the United States. It is eight times more common in men, which is due in most part to work-related exposure to asbestos. Risk also increases with age. The biggest risk factor for developing the disease is exposure to asbestos, accounting for 70 to 80 percent of all cases. Asbestos has been used in many products, including cement, brake linings, roof shingles, flooring products, textiles, and insulation. Particles can be released from these products, particularly during the manufacturing process, and inhaled. Prior to knowing the dangers, asbestos miners and other workers exposed to asbestos worked without wearing any protection. Since the 1970's, the U.S. Occupational Safety and Health Administration (OSHA) has set limits for acceptable levels of asbestos exposure and requires protective equipment in the workplace. Family members of people who worked with asbestos were also exposed to the toxin when it was carried home on clothing and hair, putting them at increased risk for mesothelioma.

Eighty percent of cases of pleural mesothelioma occur in individuals who have had known asbestos exposure, yet only 10% of people with a history of heavy exposure develop the disease. This suggests that additional exposures or factors are involved to actually develop the disease. Even more puzzling is the fact that only 50% of people with peritoneal mesothelioma have a history of asbestos exposure.

It takes 20 to 40 years from the time of asbestos exposure until mesothelioma is detected. This exposure was usually over a period of time, but has been reported to be as little as one or two months of exposure. Smoking does not seem to increase the risk of developing the disease.

The incidence of mesothelioma varies in different areas of the world, depending on when asbestos was widely used in that area. Rates are higher in the United Kingdom, where about 1800 cases per year are diagnosed. The incidence takes into consideration the number of cases and the size of the population. This is because asbestos use in Western Europe remained high until 1980, whereas maximum exposure in the U.S. was from the 1930s to 1960s. Australia was one of the world’s largest producers of asbestos, leading to the country having the highest rates worldwide (based on the size of the population). Rates in the U.S. are beginning to decline, whereas rates in Europe and Australia are expected to plateau in the next 10-15 years before declining.

Following the ban of asbestos in many countries, asbestos producers started to promote the sale of their product to developing countries, such as Asia and Latin America. Experts fear that the peak rates in these areas are yet to come, and will mimic what has been seen in the U.S. and Europe.