Mesothelioma is a rare cancer of the lining of the lung (pleural mesothelioma) or abdomen (peritoneal mesothelioma). It is usually associated with exposure to asbestos, and a majority of cases are due to occupational exposure. There are also cases due to para-occupational exposure, in which the patient is exposed to asbestos from someone else’s work, for example, the patient may be the spouse or child of an asbestos worker whose clothing is contaminated with asbestos. Studies have also investigated residential exposure, such as living in a building that contains asbestos, and environmental exposure, such as living close to an asbestos mine. A large new study has investigated specifically the effects of living in a building with loose-fill asbestos insulation[i].
In Australia, between 1968 and 1979, some houses in the Australian Capital Territory (ACT) and southern New South Wales were insulated by blowing crushed, loose-fill asbestos, largely amosite with some crocidolite, info roof spaces. In 1989-93, the ACT government surveyed approximately 65,000 houses then in existence and identified 1,089 houses with loose-fill asbestos. There was no obvious clustering of houses in particular areas.
In the new study, all residents of the Australian Capital Territory (ACT) were identified from Medicare, the Australian universal health insurance provider. Information about residents was also collected from the Australian Cancer Database and National Death Index, and linked with the list of affected addresses. Residents were classed as having ever or never lived in an affected property. Between 1 November 1983 and 31 December 2013, there were 1,035,578 ACT residents identified. Of these, 17,248 (2 %) had lived in an affected property.
The researchers investigated cases of the following cancers: mesothelioma, lung, ovarian, laryngeal, pharyngeal, stomach, colorectal, bladder, kidney, melanoma and prostate. 285 cases of mesothelioma were recorded during the study period, of which 7 (2 %) were in people diagnosed during the study period who had ever lived in an affected property. After adjusting for age and time of diagnosis, the incidence of mesothelioma in males who had lived at an affected property was 2.54 times that of unexposed males. There were an estimated 4.2 excess cases of mesothelioma in males between 1984 and 2013 due to living in an affected property. Interestingly, no mesotheliomas were reported among females who had lived at an affected property. The researchers suggest that males may have higher residential exposure than females, as a higher proportion of males than females reported entering the roof space.
Among those who lived at affected properties, there was also an elevated incidence of colorectal cancer in women and prostate cancer in men. There was also a non-significant increase in incidence of colorectal cancer in men. For lung, ovarian, laryngeal, pharyngeal and stomach cancers, which are associated with asbestos exposure, there was no evidence of an association with living in an affected building. The cause of the increased risk of colorectal cancer is uncertain; though asbestos fibres were found in living areas when the houses were inspected, and it is possible that some fibres have been ingested, there is little evidence in the literature for a link between ingestion of asbestos and colorectal cancer. The increased risk of prostate cancer was an unexpected finding, and though a causal association with residence in an affected property is plausible, further evidence is needed before any conclusions can be drawn about this observation.
A strength of this study is its large size, and a weakness is that the methods used did not allow for confounding variables such as smoking and occupational exposure to asbestos to be considered (though there is no reason to believe that occupational asbestos exposure would be different in the residentially exposed/non-exposed groups). Though the association between living in an affected property and mesothelioma in men is modest compared with that noted in studies of occupational or para-occupational exposure to asbestos, the researchers conclude that living in a house with loose-fill asbestos could be associated with some mesotheliomas in men.
[i] Korda, R. J. et al. Risk of cancer associated with residential exposure to asbestos insulation: a whole-population cohort study. The Lancet Public Health 2, e522–e528 (2017). https://www.sciencedirect.com/science/article/pii/S2468266717301925 (Accessed 28 December 2017)