Effect of smoking cessation and tobacco type on the risk of cancers of the upper aero-digestive tract in Brazil

Tobacco smoking has long been identified as the most important risk factor for upper aero-digestive tract cancers. To investigate the effect of different tobacco types and the benefit of smoking cessation, we analyzed data from a case-control study of 784 cases of mouth, pharynx, and larynx cancers and 1,578 non-cancer controls in three metropolitan hospital areas in Brazil. Subjects were interviewed as to their smoking and drinking habits, demographics, environmental exposures, occupational history, health characteristics, and diet. Controlling for total tobacco and alcohol consumption, risks for ex-smokers compared with current smokers decreased substantially with time since cessation of the habit. Compared with never smokers, ex-smokers of >20 years had a relative risk (RR) of 1.98 [95% confidence interval (CI) = 1.0-3.8] for all upper aero-digestive tract cancers. RRs for long-term (>20 years) ex-smokers tended to be lower for mouth (RR = 1.61) and pharynx (RR = 1.52) than for larynx (RR = 3.63) cancers. The benefit of quitting was strongest for commercial cigarettes (RR = 1.45, 95% CI = 0.7-3.0) for ex-smokers of >10 years, as compared with smoking of black tobacco (RR = 2.57, 95% CI = 1.4-4.6), cigars (RR = 2.59, 95% CI = 0.6-11.6), and pipe tobacco (RR = 3.40, 95% CI = 1.3-8.8).