Being a cancer, mesothelioma, or unrestrained growth and spread of the mesothelium, is, like all cancers, caused by injury to DNA that results in mutations in genes that direct cell division. The wildly growing and abnormal mesothelium can spread into adjacent tissues, or implant into remote tissues by metastasis via the circulatory or lymphatic systems. Most mesothelioma cases develop in the pleura or the perioneum (one-fifth to one-third of all cases.) The carcinogens most closely associated with mesothelioma are asbestos and smoking. Over fifty percent of people diagnosed with mesothelioma have had a history of asbestos exposure, sometimes for as little as three months. The latency period between asbestos exposure and development of mesothelioma can be as long as fifty years. Exposure to Eronite, a mineral that has a long, thin rod-like amphibole structure, has a high mortality rate due to mesothelioma in Anatolia, Turkey.
Mesothelioma is cancer of mesothelial cells, and occurs primarily in the pleural mesothelia surrounding the lungs. The mesothelia are two-layer membranes that protect most of the internal organs. About 10% of cases occur in the abdominal peritoneum, and it is also found, but less often, in heart pericardium and testicular tunica vaginalis. Prognosis is generally poor. Without treatment, median survival is 4 to 12 months, and patients that receive maximal supportive care generally survive one to two years post-diagnosis. Malignant mesothelioma is strongly linked with asbestos exposure. Inhaled asbestos fibers may damage mesothelia directly by interacting with the mitotic spindle, causing irregular cell division. Mesothelioma cell pathology includes loss of genetic material, including tumor suppressor genes likely to contribute to oncogenesis.
Mesothelioma is a malignant neoplasm that affects the mesothial surface of pleural and peritoneal cavities, most commonly the lung, but has also been found in the pericardium and tunica vaginalis. It has been linked with asbestos exposure in up to 70 % of the cases and generally presents in people 50 to 70 years old. Asbestos is still used for cement, ceiling and pool tiles, brake lining and ship building so taking a good history is important to establishing the diagnosis.
There are an estimated 2,000 to 3,000 new cases of mesothelioma each year in the United States. Mesothelioma is a rare disease. It is rare in people under age 55 and its incidence increases with age. People over 65 years old make up ¾ of people with mesothelioma. Mesothelioma is more common in white Americans than in African Americans. Men are much more likely than women to get the disease. Mesothelioma is often in an advanced stage when it is diagnosed. The average survival time is about 1 to 2 years. The 5-year relative survival rate is around 9%. The 5-year relative survival rates do not include patients dying of other diseases and are considered to be a more accurate way to describe the outcome or prognosis for patients with a particular type or stage of cancer. The 5-year survival rate refers to the percentage of patients who live at least 5 years after their cancer is diagnosed.
Exposure to asbestos has been found to be the leading cause of mesothelioma. Microscopic particles from asbestos are breathed in and travel through the airways to the alveoli. Once there, they cause damage to the cells which can cause a mesothelial cancer to form in the pleural cavity. Peritoneal mesothelioma occurs when asbestos particles are swallowed.
There have been a few documented cases of mesothelioma in people who were exposed to thorium dioxide, which was used in the past for certain types of x-rays. This has not been used for many years because of its known link to cancer.
The Simian virus has been found to cause mesothelioma in animal studies. Polio vaccines administered from the mid-1950’s to early 1960’s were found to be contaminated with this virus, though there is no definitive link between the vaccines administered during this time period and mesothelioma.
Mesothelioma is a malignant inflammation of the mesothelial cells, most commonly those covering the lung. The mesothelial coverings of the heart and abdominal cavity may also rarely be involved. This inflammation is caused by inhalation of asbestos materials, usually during prolonged occupational asbestos exposure. However, there is no minimum amount of asbestos exposure that has been correlated with development of this disease. Mesothelioma generally presents with shortness of breath and chest pain. The majority of patients with have a pleural effusion visible on plain radiographs and CT scan. However, a thoracotomy and open biopsy are generally considered the definitive method of diagnosis. Life expectancy at diagnosis is generally poor with estimations between 7 and 15 months. Treatment may include palliative care, surgical excision, or chemotherapy.
Any occupation that increases a person’s risk of exposure to asbestos would increase their risk of developing mesothelioma. Examples of these occupations include the following: shipyard workers or seamen, construction workers (especially those working in demolition), plasterers, electricians, automobile workers, insulators, and plumbers. Family members of these individuals may also be at higher risk due to possibility of asbestos fibers brought home on worker’s clothing, skin, and hair. The latency period for mesothelioma is approximately 35 to 40 years and possibly as long as 50 years. Therefore these patients typically present as men between the ages of 60 and 70 who have worked in a high-risk profession. The EPA banned any manufacturing of products that were new uses for asbestos. However, products adhering to historical uses of asbestos may still be produced. Furthermore, asbestos is still prevalent in older construction.
The most prevalent risk factor for mesothelioma is asbestos exposure. Individuals who work around asbestos are at an increased risk of developing mesothelioma. Individuals who live with a person who works around asbestos may also have an increased risk because of asbestos dust being transferred from the work environment to the home environment through clothing and hair.
While tobacco use is not directly related to mesothelioma, individuals who smoke and are also exposed to asbestos have a greater chance of developing lung disease than non-smokers who are not exposed to asbestos.
Infection with simian virus 40 (SV40) may increase the risk of developing mesothelioma. The virus was inadvertently introduced into some of the polio vaccine during the late 1950s and early 1960s. Study findings about SV40 and a possible link to cancer are conflicting; consequently, further research needs to be conducted before concluding that a connection exists between the two.