Mesothelioma is a form of cancer of the mesothelium that is primarily caused by exposure to asbestos particles. Though seventy to eighty percent of all cases of mesothelioma are reported to be a result of exposure to asbestos, there are some cases of mesothelioma where there is no such known exposure. The mesothelium is the protective sac or membrane that covers most internal organs of the body. With mesothelioma, malignant cancer cells exist in these protective sacs. Mesothelium has two distinct layers. One layer is an internal layer that immediately surrounds the organ. The second layer is an external layer that forms the sac around the organ. A lubricating fluid exists between the two layers that allows organs to move and easily glide against adjacent structures in the body. Mesothelium membranes have differing names depending on their location in the body as follows:

Peritoneum - membrane that surrounds organs in the abdominal cavity.
Pleura - membrane that surrounds the lungs and lines the walls of the chest cavity.
Pericardium – membrane that surrounds the heart.
Tunica vaginalis testis - membrane that surrounds male internal reproductive organs.
Tunica serosa uteri - membrane that surrounds female internal reproductive organs.

Most cases of mesothelioma originate in the peritoneum or pleura. The specific type of mesothelioma associated with cancer of these mesothelium include the following:

Peritoneal mesothelioma - cancer of the lining of the abdominal cavity.
Pleural mesothelioma - cancer of the lining of the pleura membrane that covers the lungs and lines the chest cavity.

Much of the research and development in the area of mesothelioma is geared towards the pleural and peritoneal forms of the cancer, which are most common. Mesothelioma of the other mesothelium membranes is rare. As such, there is limited information available for these forms of cancer.

Mesothelioma is not characterized by its own unique symptoms. Most of the symptoms of mesothelioma are characteristic of other illnesses. As such, mesothelioma has been misdiagnosed and confused with other illnesses and diseases, particularly those of the abdomen and respiratory system. To further complicate matters, the US government did not begin to track mesothelioma as a separate form of death and disease until the late 1990’s. As such, statistics, analysis, studies, etc. produced for cancer prior to the year 2000 may be misleading and inaccurate with respect to mesothelioma.

Much of the data and statistics provided for mesothelioma are based on data compiled in the Surveillance, Epidemiology and End Results (SEER) database. The 1971 National Cancer Act mandated the collection, analysis and dissemination of useful data in the prevention of, diagnosis and treatment of cancer. The SEER database was developed in response to this mandate. The SEER database is comprised of information compiled from central cancer registries in the US. These registries collect and submit cancer information and statistics, such as the incidence, prevalence, mortality, survival and stages of cancer, to the National Cancer Institute. The National Cancer Institute is responsible for the SEER database. The SEER database may be accessed at http://seer.cancer.gov/about/.

The Centers for Disease Control and Prevention (CDC) also maintains an online database, known as the Wide-ranging Online Data for Epidemiologic Research (WONDER) database. The WONDER database allows site visitors to query the database for statistical data, reports and other information that is maintained by the CDC. The WONDER database may be accessed at http://wonder.cdc.gov/.

Another widely used source of data is the US Cancer Statistics (USCS). The USCS is the official source of government statistics on cancer incidence from registries and cancer mortality data for the 50 US states as well as the District of Columbia. It includes and combines data as provided by the National Program of Cancer Registries (NPCR) and the SEER database. The NPCR is a collection of data provided by state cancer registries that may be accessed at http://www.cdc.gov/cancer/npcr/. The CDC provides support for the maintenance of these registries. NPCR data and statistics may be assessed through the CDC’s WONDER database.