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Mesothelioma Medical Information
John R. Eckardt,
MD Board Certified Oncologist Member of: American Society of Clinical Oncology American Association of Cancer Research
Malignant mesothelioma is an aggressive but rare malignancy that principally affects the pleura and peritoneum. The pleura and peritoneum are lining that cover the lung (pleura) and the abdominal cavity (peritoneum). In recent years, a steady proportional increase in pleural tumors has been matched by a proportional decrease in peritoneal tumors.[1]
Roughly 80% of cases are believed to derive from occupational or paraoccupational exposure to primary asbestos fiber types (thus the high mesothelioma asbestos claim numbers); namely, crocidolite, amosite, and chrysotile in a ratio of 500:100:1, respectively, and, less commonly, by exposure to tremolite (which has little commercial value and is therefore mined in limited quantities). These are the cases most associated with mesothelioma lawsuits and claims across the country requiring the assistance of a mesothelioma lawyer. According to recent mesothelioma statistics from Great Britain's Health and Safety Executive's Epidemiology and Medical Statistics Unit, risk appears to be highest among workers associated with the following broad areas of asbestos use: shipbuilding, railway carriage and locomotive building, and installation/maintenance of insulation materials in buildings or industrial plants.
The remaining 20% of cases have no clear-cut occupational cause and are believed to be related to etiologic factors, including contact with nonindustrial fibers such as erionite and exposure to simian virus 40 (SV40), a DNA tumor virus affecting Asian macaques that contaminated poliovirus vaccine stocks used in the late 1950s/early 1960s.
Epidemiologic Trends
Malignant mesothelioma develops after a long latency period that averages a mean of 32 years. Proportionally greater numbers of males vs females are affected (ratio approximately 3:1), and incidence follows a pattern that is defined by age and date of birth; this pattern parallels trends in asbestos exposure and associated changes in industrial consumption/use of asbestos fibers throughout the 20th century. Between 1973 and 1999, a total of 5266 mesothelioma cases were reported in the United States, at an average incidence rate of 0.97 per 100,000 people, and a higher overall incidence for men vs women (1.8/100,000 vs 0.4/100,000, respectively). Analogous to age-adjusted patterns, rates were nearly 50% higher in the 1980-1984 period compared with the 1975-1979 period, with the cohort effect peaking for males born between 1905 and 1909. Given exposure associations, the overall rate in females is unsurprisingly flat, and the estimated lifetime risk for women is 2.5 per 10,000 people. Because the use of asbestos has been banned in the United States since the 1970s, the number of male cases is expected to drop significantly during the next 50 years.
By contrast, during the same time period when asbestos was banned in the United States, asbestos imports were peaking in the United Kingdom. This accounts for the currently increasing incidence rate, from a current total of 1300 cases annually to a projected total of more than 3000 cases annually by the year 2021. In Western Europe -- specifically, Britain, France, Germany, Italy, The Netherlands, and Switzerland, which account for 75% of the entire Western European population -- asbestos use remained high until 1980, and substantial quantities are still used in several countries.
In Western Australia, crocidolite was commercially mined from 1937 to 1966, and the first cases of mesothelioma were reported in mine workers beginning in 1962. New South Wales continued to produce chrysotile until 1983, and the country as a whole continues to import about 2000 tons of chrysotile fibers a year. Consumption of asbestos in Australia peaked in 1975, which correlates with the markedly rising incidence seen over the past 20 years. More than 6000 cases were reported between 1945 and 2000 out of a total population of approximately 20 million, and an additional 600+ cases were reported in 2001 alone. Over the next 20 years, the number of cases is expected to triple, for a total of 18,000 cases by 2020.
Prognosis
when used as a radical treatment. Extrapleural pneumonectomy, defined as a "radical treatment" is associated with a median survival of 15-24 months. Extrapleural pneumonectomy involves resection of the pleura, lung, and pericardium, and often the diaphragm. Debulking parietal pleurectomy is associated with minimal morbidity and 90% effusion control at 12 months. Thoracoscopy with palliative pleurodesis is generally reserved for patients for whom pneumonectomy and other procedures (ie, pleural decortication, resection of the parietal/visceral pleura with lung preservation) are contraindicated.
RT has only been studied in limited numbers of patients, and its utility is restricted by both the volume of the tumor to be treated and by normal tissue toxicities. Like surgery, there may be a palliative role for RT, as it appears to be effective in alleviating pain. However there are no data suggesting that RT improves survival compared with best supportive care.