What Is the Main Cause of Mesothelioma?

Most cases of mesothelioma come from asbestos exposure -- more than 80 percent. Mesothelioma is a cancer of the lungs or, less commonly, the lining of the gastrointestinal tract.

Mesothelioma is a cancer that occurs when mesothelial cells that cover most internal organs grow out of control. Malignant mesothelioma commonly affects the linings of the chest or abdomen.

Malignant mesothelioma can start in four main parts of the body:

• Chest (pleural mesotheliomas)
  • This is the most common type of mesothelioma, accounting for more than 3 out of 4 cases
• Abdomen (peritoneal mesotheliomas) 
  • These account for most of the remaining cases 
• Covering around the heart (pericardial mesotheliomas) (very rare)
• Covering layer of the testicles (mesotheliomas of the tunica vaginalis) (very rare)

Malignant mesotheliomas are grouped into 3 main types based on how the cancer cells appear:

• Epithelioid
  • Accounts for more than half of all cases
  • Usually has a better prognosis than the other types
• Sarcomatoid (fibrous)
  • Accounts for about 10% to 20% of cases 
• Mixed (biphasic) mesotheliomas 
  • Have both epithelioid and sarcomatoid areas
  • Accounts for the remaining 20% to 30% of cases

Symptoms of mesothelioma vary depending on the part of the body that is affected. 

Symptoms of pleural mesothelioma (mesothelioma of the chest) include: 

• Pain in the side of the chest or lower back
• Shortness of breath
• Cough
• Difficulty swallowing
• Feeling as if something is stuck in the throat
• Hoarseness
• Swelling of the face and arms

Symptoms of peritoneal mesothelioma (mesothelioma of the abdomen) include:

• Abdominal pain
• Swelling or fluid in the abdomen
• Nausea 
• Vomiting
• Constipation

Symptoms of pericardial mesothelioma (mesothelioma of the covering around the heart) include:

• Chest pain
• Irregular heart rhythm
• Heart murmur
• Shortness of breath

General symptoms of mesothelioma include: 

• Fever
• Excessive sweating
• Fatigue
• Weight loss without trying
• Blood clots
• Loss of appetite

The main cause of pleural mesothelioma in the chest is asbestos exposure. 

• About 80% of people with mesothelioma have been exposed to high levels of asbestos
• Inhaled asbestos fibers travel to the ends of small air passages and reach the pleura and cause inflammation and scarring
• Swallowed asbestos fibers can reach the abdominal lining and may cause peritoneal mesothelioma 
• Mesotheliomas due to asbestos exposure can take between 20 to 50 years to develop

Other causes of and risk factors for developing mesothelioma include: 

• Exposure to zeolites, minerals chemically related to asbestos, such as erionite, commonly found in rocks and soil in Nevada, Oregon, Utah, Arizona, Montana, and South Dakota. It is also found in rocks and soil in Turkey. 
• Radiation therapy for cancer
• Age over 65 years 
• Being male
  • This is thought to be due to men being more likely to work in jobs with heavy exposure to asbestos
• Genetic mutations (rare)
• SV40 virus infection (this may be a factor; it is still being studied) 

Mesothelioma is diagnosed with a patient history and physical exam. Tests used to confirm the diagnosis include:

• Imaging tests
  • Chest X-ray
  • Computed tomography (CT) scan
  • Echocardiogram
  • Positron emission tomography (PET) scan
  • Magnetic resonance imaging (MRI) scan
• Blood tests
  • FIbulin-3
  • Soluble mesothelin-related peptides (SMRPs)
• Tests of fluid and tissue samples
  • Needle biopsy
  • Endoscopic biopsies
    • Thoracoscopy
    • Laparoscopy
    • Mediastinoscopy
    • Endobronchial ultrasound needle biopsy
  • Open surgical biopsy
• Pulmonary function tests

Treatment for mesotheliomas depends on the location and extent of the tumor, whether it has spread to lymph nodes or other organs, and the patients’ health and personal preferences. 

Treatments for mesothelioma may include:

• Surgery 
  • Extrapleural pneumonectomy (EPP)
  • Pleurectomy/decortication (P/D)
  • Debulking (partial pleurectomy)
• Palliative procedures 
  • Fluid removal
  • Pleurodesis
  • Shunt placement
  • Catheter placement
• Radiation therapy 
  • External beam radiation therapy (EBRT)
  • Brachytherapy
• Chemotherapy drugs
  • Pemetrexed (Alimta)
  • Cisplatin (Platinol, Platinol-AQ)
  • Cisplatin plus doxorubicin
  • Carboplatin (Paraplatin)
  • Gemcitabine (Gemzar)
  • Vinorelbine (Navelbine)
  • Paclitaxel (Taxol)
• Immunotherapy 
  • PD-1 inhibitors, including pembrolizumab (Keytruda) and nivolumab (Opdivo) 
  • CTLA-4 inhibitor such as ipilimumab (Yervoy) 
• Targeted therapy 
  • Bevacizumab (Avastin) 

Life expectancy for malignant pleural mesothelioma is often expressed in 5-year survival rates, that is, how many people will be alive 5 years after diagnosis. 

Malignant pleural mesothelioma 5-year survival rates:

• Localized (cancer is in the pleura): 20%
• Regional (cancer has spread to nearby structures or to nearby lymph nodes): 12%
• Distant (cancer has spread to distant parts of the body such as the liver, bones or pleura on the other side of the body): 8%

The biggest risk factor for developing mesothelioma is exposure to asbestos. The best way to reduce the risk of developing asbestos is to avoid or limit asbestos exposure. 

At work, make sure you use all protective equipment and follow safety procedures designed for working around asbestos.

At home, test older homes for asbestos and find out if it needs to be removed. Not all asbestos needs removal. If it does need to be removed, do not try to remove asbestos-containing material yourself. Asbestos removal should be done by a qualified contractor to avoid contaminating the home exposing your family to the asbestos.