Passive smoking and lung cancer: a publication bias?

Epidemiology of environmental tobacco smoke exposure

The health hazards due to exposure to environmental tobacco smoke (ETS) are increasingly established. ETS contains thousands of chemicals including 43 known carcinogens. One of the most important known health effects of ETS exposure is lung cancer in non-smokers, based on epidemiologic evidence and knowledge of the uptake and metabolism of ETS. Epidemiologic studies need to carefully take into account confounding and potential errors in exposure assessment. More research is needed to understand the genetic factors that influence ETS-induced lung cancer. Studies of the patterns of ETS exposure suggest higher rates of exposure in people employed as blue collar workers, in service occupations, earning lower incomes, and among the less educated. Certain racial/ethnic groups (e.g. Blacks, American Indians) may be at higher risk of ETS exposure. Despite substantial progress in protecting individuals from ETS exposure, additional efforts are needed in improving and enforcing policies to reduce exposure.

Exposure to environmental tobacco smoke and the risk of lung cancer: a meta-analysis

A meta-analysis was carried out to calculate a pooled estimate of relative risk of lung cancer following exposure to environmental tobacco smoke (ETS) and to determine whether there was any heterogeneity in the pooled estimates according to selected characteristics of the studies. A total of 35 case-control and five cohort studies providing quantitative estimates of the association between lung cancer and exposure to ETS published between January 1981 and March 1999 were identified. Using fixed- and random-effects models, we calculated pooled estimates of relative risk for exposure to ETS from subjects' parents (during childhood), spouses, and coworkers. As well, we investigated whether the pooled estimates of relative risk varied by study location, degree of control of potential confounding variables, proportion of cases confirmed histologically, proportion of surrogate respondents, nonresponse rates, and year of publication. The relative risk of lung cancer among non smoking women ever exposed to ETS from their husbands' smoking was 1.20 (95% confidence interval (CI): 1.12-1.29). The pooled relative risk was 1.19 (95% CI: 1.10-1.29) for case-control studies and 1.29 (95% CI: 1.04-1.62) for cohort studies. In various subgroup and meta-regression analyses, we found no statistically significant differences by selected characteristics of the studies. In addition, we found that the risk of lung cancer increased consistently with increasing levels of exposure. The 11 studies reporting relative risks among male non smokers yielded a pooled relative risk of 1.48 (95% CI: 1.13-1.92) for ever exposed to ETS, and the relative risk of lung cancer for ever being exposed to ETS at work was a 1.16 (95% CI: 1.05-1.28). These results are consistent with the hypothesis that exposure to ETS increases the risk of lung cancer. While there may be alternative explanations to the data, it is more likely that the observed association is not an artifact and that ETS causes lung cancer in non smokers.

Passive smoking and cancer risk: the nature and uses of epidemiological evidence

The apparent effect of passive smoking on cancer risk has become an important social and political issue. For this reason alone the strength of the epidemiological evidence warrants close examination. The research published to date indicates a positive association of passive smoking with lung cancer, but there is no consistent evidence of associations with cancer at other sites. We have summarised the epidemiological evidence, and examined the major criticisms raised against these studies. These criticisms include alleged bias arising from misclassification of exposure to environmental tobacco smoke (ETS) or of personal smoking history, and from differential publication of positive findings. In their strongest form, these critiques challenge the ability of epidemiology to establish causation on any issue. We argue that epidemiology is not inherently different from other branches of science--in each of which scientific "proof" of cause and effect involves judgement based on measurement and logical interference. We also describe the application of epidemiological data to establishing proof, in courts of law, of the lung cancer risk of passive smoking.