Objective
Most studies on tobacco smoking have focused on daily-smokers. Occasional smokers, who have never smoked daily, have often
been included in the reference group of never-smokers. We have investigated the association between occasional smoking and
cancer of the bladder, kidney, pancreas, upper aero-digestive tract and lung.
Methods
The study population consisted of 158,488 persons, who provided information on occasional smoking, within the European Prospective
Investigation into Cancer and Nutrition (EPIC), 780 of whom developed a smoking-related cancer. We used Cox proportional hazard
model, stratified by gender and country to estimate incidence rate ratios (IRR) for smoking-related cancers.
Results
The results suggest that occasional smokers have a higher risk of bladder cancer (IRR: 1.92, 95% confidence interval (CI)
0.93–3.98) and of the major smoking-related cancers combined (IRR: 1.24, 95% CI 0.80–1.94) than true never-smokers. Including
occasional smokers in the reference group resulted in a lower risk estimate for former and current smokers.
Conclusions
Occasional smoking should be discouraged.
Keywords Cancer - Cohort Study - Epidemiology - Tobacco smoke
The work described in the paper was carried out with the financial support of the “Europe Against Cancer” Programme of the
European Commission (SANCO); Deutsche Krebshilfe; German Cancer Research Center; German Federal Ministry of Education and
Research; Danish Cancer Society; Italian Association for Research on Cancer; Italian National Research Council; Dutch Ministry
of Public Health, Welfare and Sports; National Cancer Registry and the Regional Cancer Registries Amsterdam, East and Maastricht
of the Netherlands; Norwegian Cancer Society; Research Council of Norway; World Cancer Research Fund (WCRF); Swedish Cancer
Society; Swedish Scientific Council; Regional Government of Skåne, Sweden.