Use of wood stoves and risk of cancers of the upper aero-digestive tract: a case-control study

Background Incidence rates for cancers of the upper aero-digestive tract in Southern Brazil are among the highest in the world. A case-control study w as designed to identify the main risk factors for carcinomas of mouth, phar ynx, and larynx in the region. We tested the hypothesis of whether use of w ood stoves is associated with these cancers. Methods Information on known and potential risk factors was obtained from i nterviews with 784 cases and 1568 non-cancer controls. We estimated the eff ect of use of wood stove by conditional logistic regression, with adjustmen t for smoking, alcohol consumption and for other sociodemographic and dieta ry variables chosen as empirical confounders based on a change-in-estimate criterion. Results After extensive adjustment for all the empirical confounders the od ds ratio (OR) for all upper aero-digestive tract cancers was 2.68 (95% conf idence interval [CI] :2.2-3.3). Increased risks were also seen in site-spec ific analyses for mouth (OR = 2.73; 95% CI:1.8-4.2), pharyngeal (OR = 3.82; 95% CI:2.0-7.4), and laryngeal carcinomas (OR = 2.34; 95% CI:1.2-4.7). Sig nificant risk elevations remained for each of the three anatomic sites and for all sites combined even after we purposefully biased the analyses towar ds the null hypothesis by adjusting the effect of wood stove use only for p ositive empirical confounders. Conclusion The association of use of wood stoves with cancers of the upper aero-digestive tract is genuine and unlikely to result from insufficient co ntrol of confounding. Due to its high prevalence, use of wood stoves may be linked to as many as 30% of all cancers occurring in the region.