Asbestos exposure and differences in occurrence of peritoneal mesothelioma between men and women across countries

Objective

In several countries the incidence of peritoneal mesotheliomas among women closely mirrors the pattern among men. The aim was to investigate the role of asbestos exposure in the aetiology of peritoneal mesotheliomas in women and men.

Methods

All cases of peritoneal mesothelioma were selected from the Swedish and Netherlands Cancer Registers for the period 1989–2003. For both countries incidence rates were calculated and stratified by sex. A linear regression analysis was used to analyse the existence of a trend over time.

Results

Among men the incidence rate of peritoneal mesothelioma in the Netherlands (0.60 per 100?000 persons) was consistently higher than in Sweden with an average ratio of 1.8 (range 1.4–2.8). In both countries no trend over time was observed. During the 15-year period in the Netherlands the incidence rate among men was about 3.3-fold higher than among women. In Sweden the incidence rate among women was slightly higher than in men up to 1999, and thereafter about threefold higher among men. This sudden shift was statistically significant and seemed mainly caused by changes in classification of peritoneal tumours.

Conclusion

The absence of a time trend in the incidence rate of peritoneal mesothelioma in the Netherlands and Sweden in the past 15 years may point to a more limited role of occupational exposure to asbestos in the aetiology of peritoneal mesothelioma than for pleural mesothelioma, especially among women. The observed drop around 2000 in annual incidence of peritoneal mesothelioma among Swedish women indicates the presence in the past of a substantial misclassification with other tumours in the peritoneum.In many Western countries the pleural mesothelioma incidence among men has increased dramatically in the past 30 years.¹ In recent years in some countries a deceleration or leveling off of mesothelioma rates has been observed,^2,3,4 whereas in other countries the mesothelioma incidence is still expected to rise until 2020.^5,6,7 These trends have been attributed to occupational exposure to asbestos which has been substantial throughout the workforce from the 1930s up to the 1980s. It was estimated that among men with pleural mesothelioma the attributable risk was 88%.⁸ In some countries the pleural mesothelioma risk among women appears to be constant over time, suggesting that the incidence among women may be less dependent on occupational asbestos exposure.^2,5,8 It has also been suggested that the constant incidence among women implies that environmental exposure to asbestos is associated with a negligible risk⁵ or that the typical levels of environmental asbestos exposure will not exceed the threshold for mesothelioma risk.²Peritoneal mesothelioma is also linked to asbestos exposure, although with a much lower attributable risk than for pleural mesothelioma—that is, about 58% among men and less than 23% among women.⁸ Another study on elevated asbestos fibre contents in lung tissue concluded that 75% of peritoneal mesothelioma in men were most likely asbestos-related, whereas only 33% of the cases among women were attributed to asbestos exposure.⁹ It has been suggested that peritoneal mesotheliomas occur primarily among workers with higher cumulative exposures¹⁰ and that the risk increases more steeply at high exposures compared with pleural mesothelioma.^11,12 The participation of women in the industrial workforce was low, especially in occupations with high asbestos exposure such as insulators, miners and shipyard workers. Thus, a primary hypothesis would be that the peritoneal mesothelioma rates between men and women differ at least to the same extent as those for pleural mesothelioma.Trends in peritoneal mesothelioma among men and women are not as well described as trends for pleural mesothelioma. However, in the few countries with published data on trends, the annual incidence of peritoneal mesothelioma among women closely mirrors the pattern among men.^6,13,14 This surprising finding raises several important questions. First, is peritoneal mesothelioma in women the same disease as peritoneal mesothelioma among men? Second, do peritoneal mesothelioma and pleural mesothelioma differ between men and women with regard to asbestos exposure as a causal factor? The aims of this paper are to analyse differences in incidence rates of peritoneal mesothelioma in two countries and to evaluate time trends in incidence of peritoneal mesothelioma among men and women.