Malignant mesothelioma is an uncommon form of cancer. It's a disease in which cancer cells (aka malignant cells) are found in the membranes lining the lung and chest cavity (the pleura), abdomen (the peritoneum) or the heart (the pericardium).

These membranes are lined with mesothelial cells, or special cells that form tissue called mesothelium. Mesothelium protects the body’s organs. When tumors develop in the mesothelium, they can be either noncancerous (benign) or cancerous (malignant). However, most mesothelial tumors are cancerous, and malignant mesothelioma is often simply called mesothelioma.

Cases of mesothelioma can differ in terms of location (chest, abdomen, heart or a combination) and cell type (epithelioid, sarcomatoid or biphasic).

Where Is Mesothelioma?

Chest – Pleural Mesothelioma

Pleural mesothelioma is a malignant mesothelioma that spreads within the chest cavity and sometimes involves the lung. It is the most common location for mesothelioma and is usually first discovered when patients experience shortness of breath. This symptom is caused by pleural effusion, or when cancerous mesothelial cells blocks the fluid that flows through the pleura. The effusion causes fluid to build up in the lung, which makes it difficult for the patient to take a deep breath.

Abdomen – Peritoneal Mesothelioma

Even rarer than pleural mesothelioma is peritoneal mesothelioma, which affects the membranes around organs in the abdomen. Like mesothelioma in the chest, mesothelioma in the abdomen is almost always caused by exposure to asbestos.

Mesothelioma in Other Areas of the Body

Much more rarely, mesothelioma is sometimes found in the sac that surrounds the heart and in the membranes around the testicles.

What Causes Mesothelioma?

Of the patients diagnosed with mesothelioma, 80 percent were exposed to asbestos at some point in their lives. Asbestos is a family of magnesium-silicate mineral fibers. Before it was known asbestos was dangerous, it was used for insulation and in the shipbuilding and construction industries. Of workers exposed to asbestos, it's believed that 7 percent will go on to develop mesothelioma.

Exposure to asbestos does not usually cause mesothelioma right away. It's common for someone to not experience mesothelioma symptoms until 20 to 40 years after coming into contact with asbestos.

In addition to asbestos, other risk factors for mesothelioma may include:

  • Radiation (with Thorotrast contrast)
  • Exposure to the simian virus 40 (SV40)
  • Vermiculite
  • Erionite
  • Other mineral fibers (Zeolite)

Although tobacco smoke has not been associated with the development of mesothelioma, the combination of smoking and asbestos exposure greatly increases the risk for developing lung cancer.

What Are the Symptoms of Mesothelioma?

Mesothelioma symptoms vary with the severity of the condition, which varies from person to person. In most cases, mesothelioma begins very slowly. Patients do not know they have the disease until they have symptoms and see their doctors.

Pleural Mesothelioma Symptoms

The most common symptom of pleural mesothelioma is persistent pain in the chest. Sometimes this pain is accompanied by shortness of breath (or severe difficulty in breathing), cough and night sweats. Other less common symptoms are weight loss and fever.

Peritoneal Mesothelioma Symptoms

Symptoms of peritoneal mesothelioma can be vague, but the most common are abdominal pain, a swollen abdomen, weight loss, nausea and loss of appetite.

At the University of Maryland Medical Center, a thorough radiologic evaluation is performed to determine mesothelioma diagnosis. The evaluation is used to determine the stage of the tumor and to help doctors plan a course of treatment.

Testing for pleural mesothelioma may include:

  • PET/CT
  • CT scan of the chest, abdomen or pelvis
  • Biopsy to determine mesothelioma cell type and diagnosis

Because symptoms are vague, peritoneal mesothelioma is often discovered during abdominal surgery for another condition. Additional testing for peritoneal mesothelioma may include:

  • MRI of the abdomen
  • CT scan with contrast of the abdomen

Mesothelioma Subtypes

An important part of mesothelioma diagnosis is determining the cell type.

There are two types of mesothelioma cells – epithelial and sarcomatous – that result in three cellular subtypes of the disease:


More than half of mesothelioma cases involve epithelial cells. An epithelial cell has a visible nucleus – the center of a cell that functions as its "nerve center." Cells of this type have the same size and round shape and are regularly arranged.


About 1 in 10 cases are fibrous, sarcomatous cells. Unlike epithelial cells, sarcomatous cells don't have a nucleus, are elongated in shape and appear randomly.


Thirty to 40 percent of mesothelioma cases are biphasic/mixed, made up of both epithelial and sarcomatous cells.