Facts About Mesothelioma
Malignant mesothelioma is a type of cancer that affects the cells of the mesothelium.
What is the mesothelium?
The mesothelium is a membrane that lines and protects organs in the chest and in the abdominal cavity. The mesothelium has different names depending on the organs it surrounds:
- The pleura lines the lungs.
- The peritoneum surrounds the organs within the abdominal cavity.
- The pericardium envelops the heart.
- The tunica vaginalis coats the testicles.
Malignant pleural mesothelioma is a malignant or cancerous tumor of the pleura, the mesothelium that surrounds the lungs. About two of every three mesothelioma cases are pleural mesothelioma. Most of the remaining cases are mesotheliomas of the peritoneum surrounding organs in the abdominal cavity. Mesotheliomas of the membranes that surround the heart or the testicles are very rare.
MPM affects over 2,000 people a year in the U.S.; before 2030, an estimated 300,000 cases will be diagnosed. Epidemiological studies predict that approximately 250,000 Europeans will develop mesothelioma in the next few decades.
As the malignant cells grow, the pleura thickens and presses on the lungs. These changes in the pleura can make breathing difficult. Without treatment, most patients will die from mesothelioma within 4 to 12 months from the time of diagnosis. The most common causes of death are respiratory failure or pneumonia. In about one of every three patients, a small bowel obstruction develops as a result of direct extension of tumor through the diaphragm. About 1 in 10 patients die of cardiac complications when the tumor invades the pericardium and the heart.
Subtypes of MPM and Prognosis
Three subtypes of mesothelioma have been identified according to microscopic appearance:
- Epithelial - associated with the best prognosis or outcome
- Mixed types
Other factors that may predict a favorable outcome are:
- Younger age
- Good performance status
- Early-stage disease
- Lack of chest pain at diagnosis
Asbestos. Asbestos is a heat-resistant mineral used in fire-resistant and insulating materials. Exposure to asbestos is the highest risk factor for developing MPM. Between 50 percent and 80 percent of patients diagnosed with MPM are aware of exposure to asbestos at some point in their lives.
MPH affects more men than women. This is probably because more men work in industrial settings in which asbestos is common presence. The increasing incidence suggests either that the benefits of legislation to reduce asbestos exposure in the workplace have not yet taken effect, or that asbestos exposure during the 1960s was more widespread than previously believed.
Radiation. Radiation is another risk factor associated with MPM. Radiation-induced malignant mesothelioma appears to have the same prognosis as asbestos-related mesothelioma.
Genetic Factors. A significant percentage of mesothelioma patients have not been exposed to asbestos. This has led some experts to argue for a genetic predisposition. The fact that only about 5 percent of South African asbestos mine workers developed mesothelioma suggests that other environmental or genetic factors are involved.
SV-40 Virus. In addition to asbestos, some researchers have implicated exposure to the SV-40 virus, which is known to have contaminated some polio vaccines, as potentially related to this malignancy, but this has not been proven.