The effect of occasional smoking on smoking-related cancers: in the European Prospective Investigation into Cancer and Nutrition (EPIC).
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.
Bjerregaard
Bine Kjøller
BK
Institute of Cancer Epidemiology, Danish Cancer Society, Strandboulevarden 49, 2100, Copenhagen Ø, Denmark.
Raaschou-Nielsen
Ole
O
Sørensen
Mette
M
Frederiksen
Kirsten
K
Tjønneland
Anne
A
Rohrmann
Sabine
S
Linseisen
Jakob
J
Bergman
Manuela M
MM
Boeing
Heiner
H
Sieri
Sabina
S
Palli
Domenico
D
Tumino
Rosario
R
Sacerdote
Carlotta
C
Bueno-de-Mesquita
H Bas
HB
Büchner
Frederike L
FL
Gram
Inger Torhild
IT
Braaten
Tonje
T
Lund
Eiliv
E
Hallmans
Göran
G
Agren
Asa
A
Riboli
Elio
E
D000328:Adult; D000368:Aged; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000453:epidemiology*; D009749:Nutrition Surveys; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*