Academic journal article Environmental Health Perspectives

A Meta-Analysis of Asbestos and Lung Cancer: Is Better Quality Exposure Assessment Associated with Steeper Slopes of the Exposure-Response Relationships?

Academic journal article Environmental Health Perspectives

A Meta-Analysis of Asbestos and Lung Cancer: Is Better Quality Exposure Assessment Associated with Steeper Slopes of the Exposure-Response Relationships?

Article excerpt

BACKGROUND: Asbestos is a well-recognized cause of lung cancer, but there is considerable between-study heterogeneity in the slope of the exposure-response relationship.

OBJECTIVE: We considered the role of quality of the exposure assessment to potentially explain heterogeneity in exposure-response slope estimates.

Data sources: We searched PubMed MEDLINE (1950-2009) for studies with quantitative estimates of cumulative asbestos exposure and lung cancer mortality and identified 19 original epi-demiological studies. One was a population-based case-control study, and the others were industry-based cohort studies.

Data EXTRACTION: Cumulative exposure categories and corresponding risks were abstracted. Exposure-response slopes [[K.sub.L] (lung cancer potency factor of asbestos)] were calculated using linear relative risk regression models.

Data SYNTHESIS: We assessed the quality of five exposure assessment aspects of each study and conducted random effects univariate and multivariate meta-regressions. Heterogeneity in exposure-response relationships was greater than expected by chance ([I.sup.2] = 64%). Stratification by exposure assessment characteristics revealed that studies with well-documented exposure assessment, larger contrast in exposure, greater coverage of the exposure history by exposure measurement data, and more complete job histories had higher meta-[K.sub.L] values than did studies without these characteristics. The latter two covariates were most strongly associated with the [K.sub.L] value. Meta-[K.sub.L] values increased when we incrementally restricted analyses to higher-quality studies.

CONCLUSIONS: This meta-analysis indicates that studies with higher-quality asbestos exposure assessment yield higher meta-estimates of the lung cancer risk per unit of exposure. Potency differences for predominantly chrysotile versus amphibole asbestos-exposed cohorts become difficult to ascertain when meta-analyses are restricted to studies with fewer exposure assessment limitations.

Key WORDS: amphiboles, asbestos, chrysotile, lung cancer, meta-analysis. Environ Health Perspect 119:1547-1555 (2011). http://dx.doi.org/10.1289/ehp.1002879 [Online 27 June 2011]

Asbestos is a potent carcinogen that causes mesothelioma, lung cancer, and laryngeal cancer and may cause ovarian and other cancers (Straif et al. 2009). The current use of asbestos in developing countries is higher than its use in the 1960s in Western Europe and North America (U.S. Geological Survey 2009; Virta 2005). Information about exposure-response relationships is relevant for risk assessment, which is useful for developing preventive strategies. In 'Western countries, past exposures to asbestos still result in a considerable burden of disease each year (Driscoll et al. 2005; Segura et al. 2003).' This burden will remain high in the coming decades, and compensation for those exposed in the past remains an important issue.

There has long been considerable debate about the health risks associated with specific types of asbestos (McDonald and McDonald 1997; Stayner et al. 1996). Mesothelioma occurs more frequently after exposure to amphiboles than after exposure to chrysotile asbestos. The difference in mesothelioma potency, that is, the estimated risk of mesothelioma associated with a unit increase (in fiber-years) in exposure to amphibole versus chrysotile asbestos fibers, is considerable. Recent reviews support this. For example, Hodgson and Darnton (2000) found a potency ratio of 1:100:500 for chrysotile, amosite, and crocidolite, respectively, and Berman and Crump (2008a) reported estimates in the same range. In their most recent analysis, which included more mesothelioma cases from updated cohorts, Hodgson and Darnton (2010) estimated that the ratio of potency for mesothelioma was smaller: 14:1 for amosite versus chrysotile and 54:1 for crocidolite versus chrysotile.

The risk of lung cancer associated with exposure to chrysotile compared with amphibole fibers is still highly contested. …

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