What is Pleural Mesothelioma? A malignant mesothelioma that spreads within a chest cavity and can sometimes involve the lung. In addition to Asbestos, some of the other factors that can promote this disease include: tuberculous pleuritis, chronic lung infections, radiation [Thorotrast] as well as exposure to Simian Virus 40 (SV40) or Zeolite which are mineral fibers. The combination of smoking and asbestos exposure greatly increase the risk of lung cancer even though tobacco smoking has not been associated with mesothelioma development. Mesothelioma is a rare cancer which affects specific membranes of the body. About three thousand new cases of mesothelioma are diagnosed each year. The primary cause of mesothelioma is exposure to asbestos and asbestos fibers. Due to the fact that the gestation period of mesothelioma can be 20 years or more, patients who are diagnosed have a poor prognosis. The most common type of mesothelioma is pleural mesothelioma (accounting for approximately 75% of all mesothelioma cases), or mesothelioma of the pleura.The pleura is a thin serous membrane that is found between the lungs and the chest cavity. It provides a lubricated surface so that the lungs do not chafe against the chest walls, while also serving as a protective layer. Pleural mesothelioma is often incorrectly labeled as a type of lung cancer because of the pleura's close proximity to the lungs. The second most common type of mesothelioma is peritoneal mesothelioma (accounting for approximately 10% to 20% of all mesothelioma cases), or mesothelioma of the peritoneum. The peritoneum is a slippery membrane that encloses the organs of the abdomen. While peritoneal mesothelioma is less common than pleural mesothelioma, it tends to be a more invasive form of the disease, yielding a shorter life expectancy for patients. The least common type of mesothelioma is pericardial mesothelioma (accounting for less than 10% of all mesothelioma cases), or mesothelioma of the pericardium. The pericardium is the membrane that surrounds and protects the heart; it is also referred to as the heart sac. The three most common forms of mesothelioma are: Pleural mesothelioma Peritoneal mesothelioma Pericardial mesothelioma The most common cause of mesothelioma is asbestos and exposure to asbestos fibers. Most mesothelioma can be traced to one or more exposures to asbestos. This has happened in the shipyard, construction and transportation industries. There are instances where second hand exposure of asbestos fibers has been responsible for the development of mesothelioma.