STD 8 Textbook Download 2020

Mesothelioma is a type of cancer that develops from the thin layer of tissue that covers many of the internal organs (known as the mesothelium).[9] The most common area affected is the lining of the lungs and chest wall.[1][3] Less commonly the lining of the abdomen and rarely the sac surrounding the heart,[10] or the sac surrounding the testis may be affected.[1][11] Signs and symptoms of mesothelioma may include shortness of breath due to fluid around the lung, a swollen abdomen, chest wall pain, cough, feeling tired, and weight loss.[1] These symptoms typically come on slowly.[2]

More than 80% of mesothelioma cases are caused by exposure to asbestos.[3] The greater the exposure the greater the risk.[3] As of 2013, about 125 million people worldwide have been exposed to asbestos at work.[12] High rates of disease occur in people who mine asbestos, produce products from asbestos, work with asbestos products, live with asbestos workers, or work in buildings containing asbestos.[3] Asbestos exposure and the onset of cancer are generally separated by about 40 years.[3] Washing the clothing of someone who worked with asbestos also increases the risk.[12] Other risk factors include genetics and infection with the simian virus 40.[3] The diagnosis may be suspected based on chest X-ray and CT scan findings, and is confirmed by either examining fluid produced by the cancer or by a tissue biopsy of the cancer.[2]

Prevention centers around reducing exposure to asbestos.[4] Treatment often includes surgery, radiation therapy, and chemotherapy.[5] A procedure known as pleurodesis, which involves using substances such as talc to scar together the pleura, may be used to prevent more fluid from building up around the lungs.[5] Chemotherapy often includes the medications cisplatin and pemetrexed.[2] The percentage of people that survive five years following diagnosis is on average 8% in the United States.[6]

In 2015, about 60,800 people had mesothelioma, and 32,000 died from the disease.[7][8] Rates of mesothelioma vary in different areas of the world.[3] Rates are higher in Australia, the United Kingdom, and lower in Japan.[3] It occurs in about 3,000 people per year in the United States.[13] It occurs more often in males than females.[3] Rates of disease have increased since the 1950s.[3] Diagnosis typically occurs after the age of 65 and most deaths occur around 70 years old.[3] The disease was rare before the commercial use of asbestos.

The 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 the 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.[12] 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.[12][20][21] In the northern Greek mountain town of 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.[22][23]

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.[24]

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.[25]

In the United States, asbestos is considered the major cause of malignant mesothelioma[26] and has been considered "indisputably"[27] 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.[28][29][30][31] A history of asbestos exposure exists in most cases.

Pericardial mesothelioma may not be associated with asbestos exposure.[10]

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.[32] 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.[33] There appears to be a linear, dose–response relationship, with increasing dose producing increasing risk of disease.[34] Nevertheless, mesothelioma may be related to brief, low level or indirect exposures to asbestos.[27] The dose necessary for effect appears to be lower for asbestos-induced mesothelioma than for pulmonary asbestosis or lung cancer.[27] Again, there is no known safe level of exposure to asbestos as it relates to increased risk of mesothelioma.

The time from first exposure to onset of the disease, is between 25 and 70 years.[35] It is virtually never less than fifteen years and peaks at 30–40 years.[27][36] 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

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