Geography of Mesothelioma: An Overview

Claudio Bianchi, Tommaso Bianchi
Center for the Study of Environmental Cancer - Italian League against Cancer, Monfalcone, Italy

Abstract
The principal feature in mesothelioma geography is the lack of data. Reliable figures on the incidence/mortality of/from mesothelioma are available for about 15% only of the world population. In particular, mesothelioma epidemiology is scarcely known for a majority of the big asbestos producer/consumer countries. Where data are available, marked variations in incidence are observed. During the last decades mesothelioma incidence showed a progressive increase in various industrialized countries, reaching the highest values in Australia, Belgium, and the UK. In such countries, annual crude incidence rates are around 30 cases per million. At the other extreme, crude incidence rates of 0.6 and 0.7 cases per million are reported respectively from Tunisia and Morocco. Japan showed a tremendous rise in mortality from mesothelioma during the last few years. In all the countries a high ratio pleural/peritoneal is generally observed. Incidence is markedly higher among men than among women, and it varies substantially from one occupational category to another. Some occupational groups (for instance maritime trades, non asbestos textile industries) have only recently been recognized as categories at risk for mesothelioma. At the national level, wide variations are observed among the different areas. The above characteristics may largely be explained by differences in the asbestos use. The latency periods (time intervals between first exposure to asbestos and diagnosis of mesothelioma) are considerably longer than previously reported and currently appreciated. In large series mean latency periods were around 50 years. An inverse relationship between intensity of exposure to asbestos and duration of latency period has been observed. Predictions on the future trend of the mesothelioma epidemic should take into account the fact that generally latency periods are longer than 20-30 years. The mesothelioma wave consequent to the very high world asbestos consumption that occurred in the1970s has yet to be seen.

Numerous studies have recently been devoted to mesothelioma epidemiology1-11. Nevertheless, for a vast majority of countries, data on mesothelioma incidence/mortality are not available. In particular, mesothelioma epidemiology is scarcely known for various of the major asbestos producers, such as the Russian Federation, China, Kazakhstan, Brazil, and Zimbabwe. In addition, the situation is unknown for some major asbestos consumers, such as Thailand. Data are only available for about 15% of the world population. The degree of reliability such data show, varies substantially from one country to another. In fact, for some countries (e.g. Australia, Scandinavian countries, UK), the data are based on cancer registries or mesothelioma registries. In other countries, however, only limited parts are covered by registries, or mortality data only are available. Where incidence is known or may be estimated with some reliability, the rates are extremely various (Fig. 1). The highest values are reported or estimated for Australia, Belgium, and the UK.

Figure 1

In such countries the annual crude incidence rates are around 30 cases per million. The Netherlands also show high incidence (21 cases per million). A second group of countries is characterized by crude incidence rates comprised between 11 and 20 cases per million. This group includes various countries of Western and Northern Europe (France, Germany, Italy, Scandinavian countries), and New Zealand. Incidence rates below 11 cases per million are reported or estimated for many countries of Europe (Central and Eastern Europe, Iberian peninsula, Ireland), of North America (Canada, USA), Asia (Cyprus, Israel, Japan, Turkey), and Africa (Morocco, Tunisia). In a majority of countries mesothelioma incidence showed a progressive increase during the last decades. In particular, such increase was tremendous in Japan6. The lowest crude incidence rates are estimated for Morocco (0.7 cases per million), and for Tunisia (0.6 cases per million).

The principal primary site of mesothelioma is the pleura, cases originating from peritoneum being only a small percentage. The pleura/peritoneum ratio is 13:1 in Australia11; 8:1 in Japan6, and 7.3:1 in Sweden8-9. Mesothelioma incidence is markedly higher among men than among women. This fact has consistently been confirmed by studies conducted in Europe7, 9, 10, Québec4, USA5, Australia11, and Japan6. Incidence substantially varies from one occupational category to another11-12. In The Netherlands, Burdorf et al.12 have estimated that in the insulation industry, the overall risk of mesothelioma was 5 out of 100 workers, and in the shipbuilding industry, 1 out of 100 workers; in the construction industry the risk was by far lower (7 per 10,000 workers). Some occupational groups have only recently been recognized as categories at risk for mesothelioma. Epidemiological studies conducted in Finland13, Iceland14, and Sweden9 confirmed the risks existing among seafarers. Studies conducted in Italy15 show a previously unrecognized risk among non-asbestos textile industry workers. A striking feature in mesothelioma epidemiology is the strong heterogeneity in distribution at a national level. Italy offers a good example of such an irregular distribution16 (Fig. 2).

Figure 2

When the principal characteristics of mesothelioma epidemiology are considered in the frame of asbestos use history, a clear relationship emerges between asbestos consumption and mesothelioma incidence17-19. Moreover the mesothelioma distribution in a given country reflects the location of the asbestos using industries. Again Italy represents a clear example. In Italy, shipyard and port areas as well as asbestos industry areas show the highest mortality rates from pleural cancer (Fig. 2). Interestingly, in some provinces of Northern Italy with large shipyards (Genoa, Trieste, La Spezia), the high mortality rates from pleural tumors were already reported in the period 1969-197520. The marked gender difference, generally observed in mesothelioma incidence, is also adequately explained by differences in exposure to asbestos the two sexes had in various countries in the past10, 21. In many mesothelioma series, the percentages of asbestos-related cases among women are markedly lower than the cases among men. In fact, major difficulties are often encountered in reconstructing occupational and social histories in women21. However, when objective markers of asbestos exposure (pleural plaques, lung asbestos bodies) are investigated, a relationship asbestos-mesothelioma may be established also among women21. In interpreting the relationship asbestos-mesothelioma, it should be remembered that in mesothelioma, latency periods (time intervals between first exposure to asbestos and diagnosis of the tumor) may be considerably longer than previously reported and currently appreciated. In large series mean latency periods of 50 years have been reported22-24. Discrepancies among the values of latency periods in the various series may be explained by the fact that latency periods at least partly depend on the intensity of asbestos exposure22-24. People severely exposed to asbestos such as insulators show latency periods of about 30 years22-23. At the other extreme, occupational groups with less heavy exposures, such as sailors, show mean latency periods of 55 years (Figs. 3-4). Given these premises, it is clear that the effects of the highest world asbestos consumption, occurring in 1970s, remain to be seen.

Figure 3
Figure 4

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