Mesothelioma Facts

January 24, 2025

This page was reviewed under our medical and editorial policy by Jyoti Malhotra, M.D., M.P.H., associate professor, Department of Medical Oncology & Therapeutics Research, City of Hope^® Orange County Lennar Foundation Cancer Center; and Jae Y. Kim, M.D., associate professor, Division of Thoracic Surgery, Department of Surgery, City of Hope Cancer Center Duarte

Malignant mesothelioma is a rare cancer that grows in the layer of cells that line certain areas of the body, known as the mesothelium. In the United States, about 3,000 cases are diagnosed each year, according to the American Cancer Society. It is more likely to be found in older people. Mesothelioma is also more likely to be found in white, Hispanic and Latino people than in African Americans or Asian Americans.

What Is Mesothelioma?

The mesothelium is a protective membrane that lines several body cavities, such as the chest, abdomen and the space around the heart. It also surrounds organs and keeps them lubricated. The mesothelium goes by different names, depending on where in the body it is found:

• The pleura, which covers the lungs and lines the chest cavity
• The peritoneum, which covers organs in the abdomen and lines the abdominal cavity
• The pericardium, which covers the heart and lines the space around it
• The tunica vaginalis, which lines the testicles

The term mesothelioma may be used to describe any type of tumor that grows in the chest or the abdomen. These tumors may be noncancerous (benign) or cancerous (malignant). Usually, when people discuss mesothelioma, they are referring to malignant mesothelioma.

Is Mesothelioma Cancer?

Mesothelioma is named according to the area of the body affected. It is also known as malignant mesothelioma, meaning it is cancerous.

Pleural mesothelioma: This is the most common type (accounting for more than 75% of mesotheliomas) and it begins to grow in the chest. .

Peritoneal mesothelioma: This type begins to grow in the abdomen and is the second most common type of mesothelioma.

Pericardial mesothelioma: This type begins to grow in the sac around the heart.

Mesothelioma of the tunica vaginalis: This type begins to grow in the lining of the testicles.

Mesothelioma around the heart or testicles are both very rare.

Mesothelioma Causes

Mesothelioma develops when cells in the mesothelium mutate and grow out of control. They may then crowd out healthy cells and potentially spread to other body sites. Although researchers don’t always know what causes someone’s mesothelioma to develop, there are several factors that may increase risk.

Risk Factors

While researchers continue to investigate the causes of mesothelioma, several factors are already known to increase a person’s risk for the disease. They include the following.

Asbestos exposure: This is the most common risk factor for mesothelioma. Tiny fibers of asbestos can be breathed in and become lodged in lung tissue, which results in tissue inflammation and scarring. Until a few decades ago, asbestos was a common ingredient in things like building materials, steam pipes, vehicle brake shoes and plastics. Using asbestos in new materials was banned decades ago, but it still is present in the environment.

Being exposed to asbestos is the leading cause of pleural mesothelioma and may also lead to peritoneal mesothelioma if the asbestos fibers are swallowed. Many people may have been exposed without being aware of it. Sources can include home remodels or the use of talcum powder in the years before inspection standards improved.

Radiation exposure: Radiation therapy directed at the chest or abdomen, most often as a result of previous cancer treatment, increases the risk of mesothelioma.

SV40 (simian virus 40) exposure: This may be associated with developing mesothelioma. Some poliovirus vaccines administered in the 1950s and 1960s were contaminated with SV40.

Age: Older people are more likely to get cancer. For pleural mesothelioma, the average age at diagnosis is 72.

Gender: Men are more often diagnosed with mesothelioma. This is probably because many men traditionally worked in jobs with exposure to asbestos.

Erionite: This is a type of mineral similar to asbestos, which is found in rock and soil. Exposure to it may increase a person’s risk of mesothelioma. In the United States, erionite may be found in Nevada, Oregon, Utah, Arizona, Montana and South Dakota.

Genetic mutations: These may increase a person’s risk for mesothelioma. These are rare and include BAP1, NF2, CDKN2A, TP53, LATS1/2 and SETD2.

Types of Mesothelioma

Mesothelioma is classified based on how the cancer cells look under a microscope. Types are also named after where the cancer is located in a person’s body.

Epithelioid Mesothelioma

Epithelioid mesothelioma is the most common cell type. It makes up 60% to 70% of pleural mesotheliomas and 80% to 90% of peritoneal mesotheliomas, according to 2023 International Mesothelioma Interest Group guidelines. Epithelioid mesothelioma may have a better prognosis than the other cell types.

Sarcomatoid Mesothelioma

Sarcomatoid mesothelioma cell type makes up 5% to 15% of pleural mesotheliomas and less than 5% of peritoneal mesotheliomas, according to 2023 International Mesothelioma Interest Group guidelines. Another name for this type of mesothelioma is fibrous. The prognosis of sarcomatoid mesothelioma is typically worse than epithelioid.

Biphasic Mesothelioma

About 15% to 30% of pleural mesotheliomas and 10% to 20% of peritoneal mesotheliomas are biphasic cell types. This type of mesothelioma has features of both epithelioid and sarcomatoid mesotheliomas. Its prognosis is usually somewhere between that of epithelioid and sarcomatoid.

Pleural Mesothelioma

Pleural mesothelioma begins in the chest. About 3 of 4 mesotheliomas are this type.

Peritoneal Mesothelioma

Peritoneal mesothelioma, which begins in the abdomen, is the second most common type of mesothelioma.

Pericardial Mesothelioma

Pericardial mesothelioma is very rare. It begins in the sac covering the heart.

Mesothelioma of the Tunica Vaginalis

The tunica vaginalis is a layer of tissue that surrounds the testicles. This type of mesothelioma is very rare.