Tobacco Use and Cancer Risk in the Agricultural Health Study.

Background: Cigarettes are well known to cause cancer, but less is known about the risks of other tobacco products and use of more than one product. Methods: We examined cancer incidence in relation to exclusive use of six tobacco products [cigarettes, other combustibles (pipe, cigar, cigarillo), and smokeless tobacco (chewing tobacco, snuff)] in the Agricultural Health Study. We also examined the added cancer risks associated with use of cigarettes and other tobacco products. Results: In our study population of 84,015, ever use of smokeless tobacco was higher than the general United States population, whereas cigarette use was lower and other combustible product use was about the same. The strongest associations for exclusive ever use were for lung cancer [cigarettes HR = 15.48; 95% confidence interval (CI), 11.95-20.06; other combustible tobacco HR = 3.44; 95% CI, 1.53-7.71; smokeless tobacco HR = 2.21; 95% CI, 1.11-4.42]. Compared with exclusive cigarette smokers, cigarette smokers who additionally ever-used another combustible product had higher risks of smoking-related cancers (HR = 1.16; 95% CI, 1.04-1.30), especially among those who smoked cigarettes for more than 15 years. Conclusions and Impact: Cigarette smokers who additionally ever used smokeless tobacco had cancer risks similar to exclusive cigarette smokers. Users of cigarettes and other combustible tobacco may have higher risks of certain cancers than exclusive cigarette users. (C) 2016 AACR.