Smoking is now generally recognized as the most important preventable cause of human cancer and responsible for more than 230,000 new cases in North America and more than 420,000 cases annually in Europe. Passive smoking carries a lower risk and the tobacco industry has made considerable efforts to dispute the lung cancer risk associated with environmental tobacco smoke (ETS) since it is the scientific basis for legislation protecting the non-smoker at the workplace and in public spaces.

In the issue of The Lancet dated 8 April 2000, researchers from the University of California at San Francisco report the results of a review of internal documents from Phillip Morris and other tobacco companies. The documents provide evidence that the tobacco industry has closely monitored and tried to actively interfere with the conduct of an international epidemiological study on lung cancer in non-smokers following exposure to passive smoking. The study was co-ordinated by the International Agency for Research on Cancer (IARC) in Lyon, France, a research institute of the World Health Organization (WHO). The results were published in the Journal of the National Cancer Institute (Boffetta et al., J Natl Cancer Inst 90: 1440-1450; 1998) and showed that exposure to passive smoking at the workplace or through spouse results in an increased relative risk (RR) of 1.16, a small factor when compared to the RR of more than 20-fold associated with active cigarette smoking. However, given the large populations exposed to passive smoking, it has been calculated that in the USA 3000 and in Europe up to 2500 cases of lung cancer annually are caused by passive smoking.

Among the actions undertaken by the tobacco industry were the establishment of a task force to react to the publication of the results, the use of consultants to contact the IARC investigators to obtain confidential information on the study, and plans to influence the scientific policy and financing of IARC. Two years ago, the IARC study was the object of a strong defamation campaign in the media orchestrated by the tobacco industry through a lead article in the Daily Telegraph (London). Although these attacks did not pre-empt the publication of the report in the medical literature, they created confusion and controversy on the interpretation of the results. The documents reviewed in The Lancet's article suggest that this media campaign was part of a broader long-planned strategy of the tobacco industry on passive smoking.

The existence of a carcinogenic risk from passive smoking adds a new dimension to the debate on health effects of tobacco since in contrast to the diseases affecting the active smoker, it represents a health damage imposed on people who have chosen not to smoke. This difference has great implications in terms of regulation of smoking in public settings, and may, in the long run, be a major factor towards the decrease in tobacco consumption. This explains the strong interest of the tobacco industry to monitor and discredit studies, including the one from IARC, that contribute to establishing the causal link between passive smoking and cancer.