Academic journal article Scandinavian Journal of Work, Environment & Health

Lung Cancer among Coal Miners, Ore Miners and Quarrymen: Smoking-Adjusted Risk Estimates from the Synergy Pooled Analysis of Case-Control Studies

Academic journal article Scandinavian Journal of Work, Environment & Health

Lung Cancer among Coal Miners, Ore Miners and Quarrymen: Smoking-Adjusted Risk Estimates from the Synergy Pooled Analysis of Case-Control Studies

Article excerpt

Important epochs of mankind are named after the processing of stones and ores, and the industrial revolution was accompanied by the mining of iron ore and coal to a large extent. Although humans have been exposed to the health hazards from mining and stone quarrying for several thousands of years, only at the end of the 19th century have exposure circumstances in those activities been linked to lung cancer (1). A prominent example is known as Schneeberg lung disease named after a small town in the German Ore Mountains, where radon was identified as a major cause of lung cancer (1, 2).

In the second half of the 20th century, several other exposures among underground miners were identified as lung carcinogens, including arsenic, asbestos, chromium (VI), nickel, polycyclic aromatic hydrocarbons (PAH), and silica, and more recently diesel engine exhaust (3). Similarly, quarrymen may be exposed to some of these carcinogens, most typically silica. For some of these occupational risk factors of lung cancer among miners, such as asbestos and radon, more than additive synergistic effects with tobacco smoking have been established (4). The risk of lung cancer entailed in different ore mining and quarrymen settings are determined by the presence of the different lung carcinogens (depending on the minerals mined and other geological characteristics of the mines), exposure levels and their change over time (due to variations in the ores and occupational hygienic controls), potential synergistic effects with tobacco smoking, and accuracy of the study design (particularly exposure assessment and control of tobacco smoking as potential confounder and effect modifier). However, in general, miners rank high among lung cancer risks by occupational groups, as, for instance, reported by Scandinavian countries on a linkage of cancer registry and census data (5).

For coal dust, however, the same IARC working group that first classified crystalline silica as carcinogenic to humans (6) concluded that coal dust was not classifiable as to its carcinogenicity (Group 3), with inadequate evidence on cancer in humans (7). Since then, epidemiological studies have reported mixed results on lung cancer among coal miners (8-18), with extended follow-ups of cohort studies among British and US coal miners recently suggesting a positive association. However, exposure-specific results for coal dust and silica were not coherent between the two studies.

We used the SYNERGY database of pooled case- control studies on lung cancer (19-24) to estimate smoking-adjusted risks for lung cancer among coal miners, ore miners, and quarrymen (http://synergy.iarc.fr). The strengths of the SYNERGY database are detailed information on smoking behavior including the possibility to estimate pack-years of smoking as well as the full occupational history, enabling adjustment for occupational exposure to lung carcinogens from other at-risk jobs. Pooling several case-control studies conducted in different regions has the advantage that miners from a range of different settings were included and the statistical power compared to a single study is much higher.

In this study, we estimate the smoking-adjusted lung cancer risk among coal miners and compare the risk pattern with lung cancer risks among ore miners and quarrymen.

Methods

Study population

This analysis was based on 15 609 lung cancer cases and 18 531 controls from the epidemiological SYNERGY database. Only study subjects without missing values in any of the analysis variables were eligible, leaving 14 251 male cases and 17 267 male controls for data analysis (supplemental table S1, www.sjweh.fi/data_ repository.php). The study design has been described in detail elsewhere (22). We included 14 studies that were conducted in 20 study centers in Europe, Canada, and New Zealand between 1985-2010 and restricted the analysis to men, because ever working as a miner was reported by one woman only. …

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