Mesothelium
According to the National Cancer Institute, mesothelioma is a cancer that develops from the mesothelium. The mesothelium makes up a membrane that surrounds some of the body's internal organs. In the abdominal cavity, it is called the peritoneum, and in the chest, it is called the pleura. The heart is covered by a special kind of pleura called the pericardium. Mesothelium also covers the testes and the female reproductive organs (as the tunica vaginalis testis and the tunica serosa uteri, respectively). The mesothelium is made up of two layers of cells: one that is directly on top of the organs and the other that forms a little membranous sack. In between the two layers is a fluid that helps protect the organs and lubricates the two layers of the mesothelium.
Mesothelioma and Asbestos
According to the National Cancer Institute, asbestos exposure accounts for approximately 70 to 80 percent of all cases of mesothelioma (with the other cases not having an identifiable cause). Asbestos fragments or crystals can be inhaled, and they become caught in the lung tissue. Although it is not entirely understood how asbestos causes mesothelioma, the current working theory is that the asbestos fragments are able to penetrate through the lung tissue and gain access to the pleura. Asbestos can also cause mesotheliomas to develop in the peritoneum and the mesothelium that surrounds the reproductive organs, although it is not understood how it gains access to these tissues.
Cancer Development
According to the Mayo Clinic, it is not understood how asbestos exposure causes mesothelioma to develop. However, similar to all cancers, mesothelioma is the result of genetic changes that happen to the cell that make it grow uncontrollably. Because asbestos exposure also can increase the likelihood that other cancer will develop, it is thought that the asbestos fibers are able to penetrate cells and cause damage to their DNA. These genetic changes alter the way the mesothelium cells behave so they ignore signals to stop growing and instead generate their own proliferative signals.
