An overview of the risk of lung cancer in relation to exposure to asbestos and of taconite miners

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Abstract

Exposure–response relationships between the relative risk of lung cancer and quantitative measures of exposure to asbestos are available from a number of epidemiological studies. Meta-analyses of these relationships have been published by Lash et al. (1997) [Lash, T.L., Crouch, E.A.C., Green, L.C., 1997. A meta-analysis of the relation between cumulative exposure to asbestos and relative risk of lung cancer. Occup. Environ. Med. 54, 254–263] and Hodgson and Darnton (2000) [Hodgson, J.T., Darnton, A., 2000. The quantitative risks of mesothelioma and lung cancer in relation to asbestos exposure. Ann. Occup. Hyg. 44, 565–601]. In this paper, the risks derived in these meta-analyses have been compared. Lash et al., concentrated on process and found that the risk of lung cancer increased as the asbestos is refined by processing. Hodgson and Darnton concentrated on fibre type and found that the risk was highest for exposure to amphibole asbestos (crocidolite and amosite), lowest for chrysotile and intermediate for mixed exposure. Some of the differences between the conclusions from the two meta-analyses are a consequence of the choice of studies included. The range of asbestos types included in the studies in the analysis of Hodgson and Darnton was wider than that in Lash et al., enabling differences between fibre types to be analyzed more readily. There are situations where occupational exposure to chrysotile asbestos has shown no detectable increase in risk of lung cancer. Taconite miners have shown no increased risk of mortality due to lung cancer.

Introduction

The association of lung cancer with exposure to asbestos has been beyond dispute for more than 50 years following the epidemiological study of asbestos textile workers reported by Doll (1955). In the following decades there have been many studies of particular situations reported, and in some quantitative data on exposure have been available allowing consideration of exposure–response relationships. The more recent work on quantitative exposure–response relationships has enabled risk estimates to be derived including estimates due to environmental exposure based on direct study in addition to extrapolation from occupational situations.

Section snippets

Meta-analyses and measures of effect

Meta-analyses of exposure–response relationships between the relative risk (RR) of lung cancer and cumulative exposure to asbestos (d) have been published by Lash et al. (1997) and by Hodgson and Darnton (2000). Lash et al. included 15 cohorts, and fitted the linear dose–response model within each cohort:RR=A(1+kd)where A is an intercept term, that is the relative risk for zero exposure, k is the slope, or increase in relative risk per unit of exposure, and d is the cumulative exposure

Comparison of “Lash et al.” and “Hodgson and Darnton”

There were 11 studies in common to the two meta-analyses so that the values may be compared:

  • 1.

    Paterson insulation factory processing amosite (Seidman et al., 1986);

  • 2.

    Ontario asbestos cement plant using chrysotile and crocidolite (Finkelstein, 1984);

  • 3.

    Pennsylvania textile factory processing mainly chrysotile and amosite (McDonald et al., 1983);

  • 4.

    Vöcklabruck asbestos cement factory using chrysotile and crocidolite (Neuberger and Kundi, 1990);

  • 5.

    Rochdale male textile factory workers processing mainly

Problems in estimating exposure

There are uncertainties in the measurements of exposure, arising from changes in instrumentation, problems in conversion of results obtained using old types of instruments to modern methods, a lack of systematic sampling in early years, and consequentially the use of “guestimates” of early exposure (Rogers, 2001). A consequence of this is that exposure–response relationships which may be qualitatively valid within a study because relative exposure levels are reasonable, can be invalid outside

Taconite and cummingtonite–grunerite

A cohort study of miners at the Reserve Mining Company was reported by Higgins et al. (1983). Five thousand seven hundred and fifty-one workers employed for a year or more between 1952 and 1976 were followed up until 1976 (a maximum of 24 years). For all causes of death there were 298 deaths, compared with an expected number of 344 (SMR = 87). For mortality due to respiratory cancer, there were 15 observed deaths, compared with an expected number of 18 (SMR = 84). These include deaths soon after

Environmental exposure

Camus et al. (1998) reported a study of women living in two chrysotile asbestos mining areas in Quebec, over the period 1970–1989. The average cumulative exposure was estimated as 25 fibres/ml years, with a plausible range from 5 to 125 fibres/ml years, equivalent to 105 fibres/ml working years, after converting to the measure used for occupational exposure over 40 h a week.

There had been 71 deaths due to lung cancer, compared with 71.4 expected from rates in unexposed areas. Predictions based on

Risk at low exposure

A linear dose–response relationship between relative risk of lung cancer and exposure is often used (“a widely accepted and scientifically reasonable compromise rather than an established scientific principle” (HEI, 1991)). Non-linearity and/or the existence of a threshold at low levels of exposure are very difficult, perhaps impossible, to detect from epidemiological data (Liddell, 2001). Depending on the potency of the agent low exposures can result in risks that are so low that they are

Summary

Asbestos exposure increases lung cancer incidence. There are situations where occupational exposure to chrysotile asbestos has shown no detectable increase in risk. Taconite miners have shown no increased risk of mortality due to lung cancer.

Conflict of Interest

Dr Berry has given opinions in asbestos-related disease compensation cases. Dr Gibbs has appeared as an expert witness in asbestos-related litigation cases. Several years ago Dr Gibbs provided consultation services to an organization representing the Taconite Industry.

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