The Epidemiology of Tobacco and Lung Cancer: Some Conclusions from a Lifetime of Research

Abstract

This review summarizes evidence on the smoking/lung cancer relationship, based on the author's 50 years' experience. It starts by illustrating variations in national rates by time and sex. It then demonstrates that the relationship of smoking to overall lung cancer risk is strong, consistently seen and dose-related with amount smoked, duration, age of start and time of quitting. Relative risks vary markedly by country, but little by sex, age, race, occupation, genetics and other factors. Though precisely estimating the smoking risk is difficult, the relationship is clearly causal, not explained by bias or confounding. The risk from smoking is reduced in lower tar filter cigarettes, and essentially independent of mentholation and type of curing. Lung cancer risk is not increased by smokeless tobacco use. The relative risk is much greater for squamous/small-cell carcinoma than for adeno/ large-cell carcinoma. The argument that the increasing ratio of squamous to adenocarcinoma results from changes in cigarettes is shown to be weak, the increase also being seen in never smokers, starting before filters were introduced, and associated with diagnostic changes. Most of the weak association of lung cancer with passive smoking is explicable by confounding and by misclassification of some ever smokers as never smokers.