Involuntary Smoking and the Risk of Head and Neck Cancer in an East Asian Population.

Background: Although tobacco involuntary smoking is an established risk factor for lung cancer, the association with head and neck cancer (HNC) is not established. We aimed to investigate this potential association in an East Asian population. Methods: We conducted a multicenter case-control study in East Asia including eight centers. We restricted our analysis to never tobacco smokers (303 cases and 459 controls) and to never tobacco smokers/never alcohol drinkers (243 cases and 403 controls). Results: Among never tobacco smokers, involuntary smoking was associated with a 1.47-fold increase in risk of HNC (95%CI = 1.02, 2.13) and a 1.8-fold increase in the risk of oral cavity cancer (95%CI = 1.14, 2.92). Among never tobacco smokers who were also never alcohol drinkers, increased risks were detected for more than 3 h per day of involuntary smoking exposure and for 15 or more years of exposure. A dose-response relation was suggested for frequency of exposure (p for trend = 0.014) and for years of exposure (p for trend = 0.010) for oral cavity cancer. We did not detect strong increases in the risk of the other HNC subsites. Conclusions: Our study supports the association between involuntary smoking and the risk of HNC. The association may be stronger for oral cavity cancer than for other HNC subsites.