A group of Italian researchers have investigated the epidemiology of mesothelioma in women[i]. Mesothelioma is a rare tumour, usually associated with exposure to asbestos. It is more common in males than in females, because greater numbers of males were occupationally exposed. In the literature, mesothelioma in women has been reported to be due to occupational exposure, para-occupational exposure (exposure to, for example, a partner or parent’s asbestos-contaminated clothing), and environmental exposure.
Data on incident mesothelioma cases between 1993 and 2012 were retrieved from the Italian national register. The ratio of female to male mesothelioma cases was determined, and compared to that of other countries. The economic activity sectors, jobs and geographical distribution of female cases of mesothelioma were also investigated.
During the period of interest, there were 21,463 malignant mesotheliomas registered, of which the type of asbestos exposure was investigated in 76.7 %. Among the male mesothelioma incident cases for which exposure was assessed, 86.9 % had been exposed to asbestos, and 95 % of these were exposed occupationally. Among females, 61.4 % of assessed cases were exposed to asbestos.
Overall, about 28 % of mesothelioma cases in Italy occurred in females. The overall ratio of female to male cases was 0.38 for pleural mesothelioma and 0.70 for peritoneal mesothelioma (i.e. 38 female cases for every 100 male cases and 70 female cases for every 100 male cases, respectively). Among occupationally exposed cases the gender ratios are 0.14 and 0.30 for pleural and peritoneal mesothelioma, respectively, meaning that a smaller proportion of cases occurred in females when only occupationally exposed patients are included in the analysis. The female to male ratio is much higher in cases of non-occupational origin (familial, environmental or leisure exposure), for example, for familial exposure there were almost 6 pleural and 11 peritoneal female cases for every male case.
Occupational asbestos exposures in female cases were in the chemical and plastic industry, and mainly in the non-asbestos textile sector. The latter was identified as causing asbestos exposure in more than 40 % of both pleural and peritoneal mesothelioma cases in females with occupational asbestos exposure. Occupational exposure in this sector is mainly due to the widespread use of operating machines with asbestos-containing friction materials, and asbestos products such as anti-condensation materials in buildings. Jobs in which women were exposed to asbestos include farmers, tailors and dressmakers, ironers, clerks and teachers.
In cases with unknown or not probable asbestos exposure, the ratio of female to male cases was 1.03 for pleural and 1.48 for peritoneal cases of mesothelioma, respectively. These are significantly greater (larger proportion of female cases) than the overall ratios. Among the pleural mesothelioma cases for which asbestos exposure was investigated, around 38 % and 13 % of female and male cases were classed as having unknown or not probable exposure. The corresponding figures for peritoneal mesothelioma are 47 % in females and 21 % in males. These figures are sufficiently high to call into question the common statement that “all or almost all cases of mesothelioma are caused by asbestos”.
The ratio of female to male cases was inversely associated with the mesothelioma mortality rate, when different countries were compared. In other words, the countries with the highest mortality due to mesothelioma had the smallest proportions of cases in females. The percentage of female cases among mesothelioma deaths varied from 10.6 % in Denmark to 43.5 % in Turkey. This finding indicates that the countries with higher industrial use of asbestos in the past had larger numbers of exposed workers in male-dominated occupational sectors, resulting in far more cases in males than in females. Italy is something of an anomaly within this data, having a higher proportion of cases in women than expected for its mortality rate. This is perhaps due to Italy being one of the leading producers of textiles, leading to the high numbers of cases in females employed in the non-asbestos textile sector.
The researchers conclude that non-occupational asbestos exposure plays an important role in female mesothelioma, along with the historical female workforce in the non-asbestos textile industry and in other sectors in which asbestos exposure was possible. In addition, significant proportions of cases investigated for asbestos exposure were found to have unknown or not probable exposure.
[i] Marinaccio, A. et al. The epidemiology of malignant mesothelioma in women: gender differences and modalities of asbestos exposure. Occup Environ Med (2017). doi:10.1136/oemed-2016-104119 http://oem.bmj.com/content/early/2017/12/21/oemed-2016-104119 (Accessed 28 December 2017)