Most people who develop mesothelioma have worked in careers such as mining, where they inhaled or ingested asbestos fibers, or were exposed to airborne asbestos dust and fibers in other ways. Washing the clothing of a family member who worked with asbestos also creates a risk for developing mesothelioma.[5]
Signs and symptoms of mesothelioma include shortness of breath due to pleural effusion (fluid between the lung and the chest wall), chest wall pain and constitutional signs such as unexplained weight loss. The diagnosis may be suspected based on chest X-ray and CT scan findings, but must be confirmed either by examining serous effusion cytology or with a biopsy (removing a sample of the suspicious tissue). A thoracoscopy (inserting a tube with a camera into the chest) can be used to acquire biopsy material, and allows the introduction of substances such as talc to obliterate the pleural space (a procedure called pleurodesis), preventing more fluid from accumulating and pressing on the lung. Despite treatment with chemotherapy, radiation therapy or sometimes surgery, mesothelioma carries a poor prognosis. Research about screening tests for the early detection of mesothelioma is ongoing.
Signs and symptoms[edit]
Symptoms or signs of mesothelioma may not appear until 20 to 50 years (or more) after exposure to asbestos. Shortness of breath, cough, and pain in the chest due to an accumulation of fluid in the pleural space (pleural effusion) are often symptoms of pleural mesothelioma.[6]
The most common symptoms of peritoneal mesothelioma are abdominal swelling and pain due to ascites (a buildup of fluid in the abdominal cavity). Other features may include weight loss, fever, night sweats, poor appetite, vomiting, constipation, and umbilical hernia.[7] If the cancer has spread beyond the mesothelium to other parts of the body, symptoms may include pain, trouble swallowing, or swelling of the neck or face.[citation needed]
These symptoms may be caused by mesothelioma or by other, less serious conditions.
Mesothelioma that affects the pleura can cause these signs and symptoms:[6]
Chest wall pain
Pleural effusion, or fluid surrounding the lung
Shortness of breath
Fatigue or anemia
Wheezing, hoarseness, or cough
Blood in the sputum (fluid) coughed up (hemoptysis)
In severe cases, the person may have many tumor masses. The individual may develop a pneumothorax, or collapse of the lung. The disease may metastasize, or spread to other parts of the body.[citation needed]
Tumors that affect the abdominal cavity often do not cause symptoms until they are at a late stage. Symptoms include:[citation needed]
Abdominal pain
Ascites, or an abnormal buildup of fluid in the abdomen
A mass in the abdomen
Problems with bowel function
Weight loss
In severe cases of the disease, the following signs and symptoms may be present:[citation needed]
Blood clots in the veins, which may cause thrombophlebitis
Disseminated intravascular coagulation, a disorder causing severe bleeding in many body organs
Jaundice, or yellowing of the eyes and skin
Low blood sugar level
Pleural effusion
Pulmonary emboli, or blood clots in the arteries of the lungs
Severe ascites
A mesothelioma does not usually spread to the bone, brain, or adrenal glands. Pleural tumors are usually found only on one side of the lungs.[citation needed]
Pericardial mesothelioma is not well characterized, but observed cases have included cardiac symptoms, specifically constrictive pericarditis, heart failure, pulmonary embolism, and cardiac tamponade. They have also included nonspecific symptoms, including substernal chest pain, orthopnea (shortness of breath when lying flat), and cough. These symptoms are caused by the tumor encasing or infiltrating the heart.[3]
Cause[edit]
Working with asbestos is the most common risk factor for mesothelioma.[8] In the United States, asbestos is considered the major cause of malignant mesothelioma[9] and has been considered "indisputably"[10] associated with the development of mesothelioma. Indeed, the relationship between asbestos and mesothelioma is so strong that many consider mesothelioma a “signal” or “sentinel” tumor.[11][12][13][14] A history of asbestos exposure exists in most cases. However, mesothelioma has been reported in some individuals without any known exposure to asbestos. In rare cases, mesothelioma has also been associated with irradiation of the chest or abdomen, intrapleural thorium dioxide (thorotrast) as a contrast medium, and inhalation of other fibrous silicates, such as erionite or talc.[4][15] Some studies suggest that simian virus 40 (SV40) may act as a cofactor in the development of mesothelioma.[15] This has been confirmed in animal studies,[16][17] but studies in humans are inconclusive.[16][18][19] Pericardial mesothelioma may not be associated with asbestos exposure.[3]
Asbestos was known in antiquity, but it was not mined and widely used commercially until the late 19th century. Its use greatly increased during World War II. Since the early 1940s, millions of American workers have been exposed to asbestos dust. Initially, the risks associated with asbestos exposure were not publicly known. However, an increased risk of developing mesothelioma was later found among naval personnel (e.g., Navy, Marine Corps and Coast Guard), shipyard workers, people who work in asbestos mines and mills, producers of asbestos products, workers in the heating and construction industries, and other tradespeople. Today, the official position of the U.S. Occupational Safety and Health Administration (OSHA) and the U.S. EPA is that protections and "permissible exposure limits" required by U.S. regulations, while adequate to prevent most asbestos-related non-malignant disease, are not adequate to prevent or protect against asbestos-related cancers such as mesothelioma.[20] Likewise, the British Government's Health and Safety Executive (HSE) states formally that any threshold for exposure to asbestos must be at a very low level and it is widely agreed that if any such threshold does exist at all, then it cannot currently be quantified. For practical purposes, therefore, HSE assumes that no such "safe" threshold exists. Others have noted as well that there is no evidence of a threshold level below which there is no risk of mesothelioma.[21] There appears to be a linear, dose-response relationship, with increasing dose producing increasing disease.[22] Nevertheless, mesothelioma may be related to brief, low level or indirect exposures to asbestos.[10] The dose necessary for effect appears to be lower for asbestos-induced mesothelioma than for pulmonary asbestosis or lung cancer.[10] Again, there is no known safe level of exposure to asbestos as it relates to increased risk of mesothelioma.
The duration of exposure to asbestos causing mesothelioma can be short. For example, cases of mesothelioma have been documented with only 1–3 months of exposure.[23][24] People who work with asbestos wear personal protective equipment to lower their risk of exposure.[citation needed]
Latency, the time from first exposure to manifestation of disease, is prolonged in the case of mesothelioma. It is virtually never less than fifteen years and peaks at 30–40 years.[10] In a review of occupationally related mesothelioma cases, the median latency was 32 years.[25] Based upon the data from Peto et al., the risk of mesothelioma appears to increase to the third or fourth power from first exposure.[22]
Environmental exposures[edit]
Incidence of mesothelioma has been found to be higher in populations living near naturally occurring asbestos. People can be exposed to naturally occurring asbestos in areas where mining or road construction is occurring, or when asbestos-containing rock is naturally weathered. Another common route of exposure is through asbestos-containing soil, which is used to whitewash, plaster, and roof houses in Greece.[5] In central Cappadocia, Turkey, mesothelioma was causing 50% of all deaths in three small villages—Tuzköy, Karain and Sarıhıdır. Initially, this was attributed to erionite. Environmental exposure to asbestos has caused mesothelioma in places other than Turkey, including Corsica, Greece, Cyprus, China, and California.[5][26][27] In Metsovo, this exposure had resulted in mesothelioma incidence around 300 times more than expected in asbestos free populations and was associated with very frequent pleural calcification known as "Metsovo Lung".[28][29]
The documented presence of asbestos fibers in water supplies and food products has fostered concerns about the possible impact of long-term and, as yet, unknown exposure of the general population to these fibers.[citation needed]
Exposure to talc is also a risk factor for mesothelioma; exposure can affect those who live near talc mines, work in talc mines, or work in talc mills.[15]
Occupational[edit]
Exposure to asbestos fibers has been recognized as an occupational health hazard since the early 20th century. Numerous epidemiological studies have associated occupational exposure to asbestos with the development of pleural plaques, diffuse pleural thickening, asbestosis, carcinoma of the lung and larynx, gastrointestinal tumors, and diffuse malignant mesothelioma of the pleura and peritoneum. Asbestos has been widely used in many industrial products, including cement, brake linings, gaskets, roof shingles, flooring products, textiles, and insulation.[citation needed]
Commercial asbestos mining at Wittenoom, Western Australia, took place from 1937 to 1966. The first case of mesothelioma in the town occurred in 1960. The second case was in 1969, and new cases began to appear more frequently thereafter. The lag time between initial exposure to asbestos and the development of mesothelioma varied from 12 years 9 months up to 58 years.[30] A cohort study of miners employed at the mine reported that 85 deaths attributable to mesothelioma had occurred by 1985. By 1994, 539 reported deaths due to mesothelioma had been reported in Western Australia.[citation needed]
Occupational exposure to asbestos in the United States mainly occurs when people are maintaining buildings that already have asbestos. Approximately 1.3 million US workers are exposed to asbestos annually; in 2002, an estimated 44,000 miners were potentially exposed to asbestos.[15]
Paraoccupational secondary exposure[edit]
Family members and others living with asbestos workers have an increased risk of developing mesothelioma, and possibly other asbestos related diseases.[4][31][32] This risk may be the result of exposure to asbestos dust brought home on the clothing and hair of asbestos workers via washing a worker's clothes or coming into contact with asbestos-contaminated work clothing.[5][15] To reduce the chance of exposing family members to asbestos fibres, asbestos workers are usually required to shower and change their clothing before leaving the workplace.[citation needed]
Asbestos in buildings[edit]
Many building materials used in both public and domestic premises prior to the banning of asbestos may contain asbestos. Those performing renovation works or DIY activities may expose themselves to asbestos dust. In the UK use of Chrysotile asbestos was banned at the end of 1999. Brown and blue asbestos was banned in the UK around 1985. Buildings built or renovated prior to these dates may contain asbestos materials.[citation needed]
Genetic disposition[edit]
In a recent research carried on white American population in 2012, it was found that people with a germline mutation on their BAP1 gene are at higher risk of developing mesothelioma and uveal melanoma.[33]
Erionite[edit]
Main article: Erionite
Erionite is a zeolite mineral with similar properties to asbestos and is known to cause mesothelioma.[4] Detailed epidemiological investigation has shown that erionite causes mesothelioma mostly in families with a genetic predisposition.[5][26][27] Erionite is found in deposits in the Western United States, where it is used in gravel for road surfacing, and in Turkey, where it is used to construct homes. In Turkey, the United States, and Mexico, erionite has been associated with mesothelioma and has thus been designated a "known human carcinogen" by the US National Toxicology Program.[27]