The most important causal factor for the development of human mesothelioma is exposure to asbestos, primarily the amphiboles croci-dolite and amosite. Malignant mesothelioma is presently a worldwide
Table 2.1. Types, composition and characteristics of asbestos fibers
Type Composition Source Morphology
Type Composition Source Morphology
Chrysotile* Mg6Si4O10 (OH)8 Northern hemisphere Curly, pliable
(U.S. and Canada)
Crocidolite Na2(Fe3+)2(Fe2+) South Africa, Rodlike, durable
3Si8O22(OH)2 Western Australia
Amosite (Fe, Mg)7Si8O22(OH)2 South Africa Rodlike, durable
Anthophyllite (Mg, Fe)7Si8O22(OH)2 Finland Rodlike, durable
Tremolite Ca2Mg5Si8O22(OH)2 Exists in some deposits of Rodlike, durable
Canadian chrysotile
Actinolite Ca2(Mg, Fe)5Si8O22(OH)2 Not mined
* Only member of the “serpentine” family. Other types of asbestos are classified as “amphiboles.”
3Si8O22(OH)2 Western Australia
Amosite (Fe, Mg)7Si8O22(OH)2 South Africa Rodlike, durable
Anthophyllite (Mg, Fe)7Si8O22(OH)2 Finland Rodlike, durable
Tremolite Ca2Mg5Si8O22(OH)2 Exists in some deposits of Rodlike, durable
Canadian chrysotile
Actinolite Ca2(Mg, Fe)5Si8O22(OH)2 Not mined
* Only member of the “serpentine” family. Other types of asbestos are classified as “amphiboles.”
problem (5). Although mesothelioma is a rare disease, with an annual incidence in the United States of 2000 to 3000 cases, a steady rise in cases has been reported (6). In Europe, the incidence of malignant pleural mesothelioma has risen for decades and is expected to peak between the years 2010 and 2020 (7). In Germany, a study conducted on 1605 patients in the mesothelioma register (1987–1999), found that 70% had a history of exposure to asbestos (8). In the United Kingdom, asbestos reportedly accounts for some 600 cases of mesothelioma and
100 cases of bronchial carcinoma per year (9). The incidence of mesothelioma has been rapidly increasing and is expected to increase even more from the present total of 1300 to more than 3000 cases per year. Exposure to fibers is associated with most of these cases (10).
The link between amphibole asbestos exposure and pleural mesothe-ioma is the result of the pioneering work of Wagner and colleagues (11), who found a relationship between the high incidence of the dis-ease and people working at or living near crocidolite (blue) asbestos
mines, with intermediate levels of disease near amosite mines, and no tumors in chrysotile miners.
100 cases of bronchial carcinoma per year (9). The incidence of mesothelioma has been rapidly increasing and is expected to increase even more from the present total of 1300 to more than 3000 cases per year. Exposure to fibers is associated with most of these cases (10).
The link between amphibole asbestos exposure and pleural mesothe-ioma is the result of the pioneering work of Wagner and colleagues (11), who found a relationship between the high incidence of the dis-ease and people working at or living near crocidolite (blue) asbestos
mines, with intermediate levels of disease near amosite mines, and no tumors in chrysotile miners.
Lung burden studies (see Chapter 1) have also confirmed that the amphibole subgroup of asbestos (crocidolite, amosite) is the one more strongly associated with the development of both malignant meso-thelioma and lung cancers (12). In a recent study on 1445 cases of mesothelioma in the United States, it was determined that commercial amphiboles were responsible for most of the mesothelioma cases observed (13). Chrysotile asbestos may produce mesothelioma in humans, but the number of cases is small and the required exposures
large (12). Heavy exposures to chrysotile asbestos alone, or with neg-ligible amphibole contamination, can cause malignant mesothelioma and other lung cancers in humans (14), but studies evaluating worker populations that are transient and may be exposed to different types
of fibers over a lifetime are difficult to interpret.
Some studies have implicated tremolite fibers as the likely etiologic factor in mesotheliomas associated with chrysotile exposure (15–17).
However, others suggest that chrysotile does cause mesothelioma, although it may be far less potent than amphibole asbestos (18). Although the association between amphibole asbestos exposure and the development of malignant mesothelioma is well documented (19), available information suggests that other factors contribute to its etiol- ogy. Some studies suggest that genetic factors may play an important
role in the etiology of the disease (20,21). Also, compelling multiinstitu-tional studies suggest that SV40 tumor (T)-antigen (Tag) is present in a large percentage of human mesotheliomas. Approximately 60% of mesotheliomas in the United States are positive for SV40 Tag (22,23), and possible mechanisms are discussed in other chapters of this volume (see
Chapter 3).
Epidemiology of Asbestos-Induced Mesotheliomas
large (12). Heavy exposures to chrysotile asbestos alone, or with neg-ligible amphibole contamination, can cause malignant mesothelioma and other lung cancers in humans (14), but studies evaluating worker populations that are transient and may be exposed to different types
of fibers over a lifetime are difficult to interpret.
Some studies have implicated tremolite fibers as the likely etiologic factor in mesotheliomas associated with chrysotile exposure (15–17).
However, others suggest that chrysotile does cause mesothelioma, although it may be far less potent than amphibole asbestos (18). Although the association between amphibole asbestos exposure and the development of malignant mesothelioma is well documented (19), available information suggests that other factors contribute to its etiol- ogy. Some studies suggest that genetic factors may play an important
role in the etiology of the disease (20,21). Also, compelling multiinstitu-tional studies suggest that SV40 tumor (T)-antigen (Tag) is present in a large percentage of human mesotheliomas. Approximately 60% of mesotheliomas in the United States are positive for SV40 Tag (22,23), and possible mechanisms are discussed in other chapters of this volume (see
Chapter 3).
Epidemiology of Asbestos-Induced Mesotheliomas
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