Interaction between tobacco and alcohol consumption and the risk of cancers of the upper aero-digestive tract in Brazil

The authors investigated the joint effects of tobacco and alcohol consumpti on on the risk of squamous cell carcinomas of the upper aero-digestive trac t (UADT) using data from a hospital-based case-control study conducted in s outhern Brazil, 1986-1989. A total of 784 cases of cancers of the mouth, ph arynx, and larynx and 1,578 non-cancer controls matched on age, sex, hospit al catchment area, and period of admission were interviewed about their smo king and drinking habits and other characteristics. Using logistic regressi on, evidence was found for interaction between the cumulative exposures for smoking and alcohol on UADT cancer risk. The joint effects for pharyngeal cancers exceeded the levels expected under a multiplicative model for moder ate smokers (p = 0.007). There was little statistical evidence, however, fo r interaction on cancers of the mouth (p = 0.28) or larynx (p = 0.95). Amon g never smokers, heavy drinkers had 9.2 times (95% confidence interval 1.7, 48.5) greater risk of cancers of mouth, pharynx, and supraglottis than nev er drinkers, with a dose-response trend (p = 0.013) with cumulative consump tion. The authors conclude that the interaction occurring in the pharynx be tween smoking and alcohol on UADT cancers is not uniform, with varying effe cts depending on the level of smoking exposure. Alcohol may act as both a p romoter for tobacco and as an independent risk factor.