Mesothelioma, or malignant mesothelioma, is a cancer that occurs in the mesothelium, a protective tissue that covers many organs in the body. There are several types of mesothelioma, each named for the particular area of the body affected, including:
- Pleural mesothelioma (the lining of the lungs)
- Peritoneal mesothelioma (the lining of the abdominal cavity)
- Pericardial mesothelioma (the sac that encases the heart)
- Mesothelioma of the tunica vaginalis testis (the lining of the internal male sex organs)
- Mesothelioma of the tunica serosa uteri (the lining of the internal female sex organs)
Pleural mesothelioma is the most common type of mesothelioma, representing about 75 percent of all cases. Pleural mesothelioma is usually caused by inhaling asbestos fibers, which become trapped in the pleura and cause scarring and inflammation. After a long latency period of 30 to 50 years, cancer develops.
Because the lung is the site of other more common diseases, such as pneumonia and lung cancer, pleura mesothelioma may be initially misdiagnosed.
The second most common type of mesothelioma is peritoneal mesothelioma, accounting for 10 to 20 percent of mesothelioma cases. This type of mesothelioma develops in the peritoneum, the tissue that lines the abdomen. Peritoneal mesothelioma occurs if a carcinogen — usually an asbestos fiber — is ingested, which can happen when an inhaled particle finds its way into the esophagus and then gets lodged in the digestive tract. Some cases of peritoneal mesothelioma have been linked to exposure to another silicate fiber called erionite, as well as to Thorotrast, a radioactive contrast medium used for X-rays prior to the 1950s.
Peritoneal mesothelioma has a latency period may be somewhat shorter than for pleural mesothelioma, developing 20 to 30 years after exposure.
Pericardial mesothelioma, which occurs in the tissue lining the heart, accounts for less than 10 percent of cases worldwide. Like the more common types of mesothelioma, it is associated with asbestos exposure. It can be caused by cancer cells from pleural mesothelioma breaking through the pleura and into the pericardium. It is not clear exactly how inhaled, or even swallowed, asbestos particles make their way to the pericardium to cause pericardial mesothelioma as a primary cancer. One theory suggests that asbestos fibers in the lungs may eventually break down, seep into the bloodstream, and then become lodged in the heart. Another possibility is that genetic factors increase the risk of pericardial mesothelioma.
“If there is a genetic predisposition to the disease, it would be present in any of the cells of the body,” including pericardial cells, explains Timothy Winton, MD, associate professor of surgery and division director of thoracic surgery of the University of Alberta and University of Alberta Hospital, Edmonton, Canada. “It may be that these other forms of [mesothelioma] are triggered by the central exposure at the lung and pleural space levels, causing inflammatory responses at the disease site.”
Mesothelioma of the Tunica Vaginalis Testis and of the Tunica Serosa Uteri
Mesothelioma involving the reproductive tissues is the rarest of all forms of the disease. Mesothelioma of the tunica vaginalis testis — the lining around the male testes — and mesothelioma of the tunica serosa uteri — the lining of the female sex organs — account for fewer than 100 cases in all the medical literature. Many of the more recently diagnosed cases of this type of mesothelioma have been linked to asbestos exposure.
Though there are a few different types of mesothelioma, it remains a rare form of cancer.