Invited Commentary: Smokeless Tobacco-An Important Contributor to Cancer, but More Work Is Needed.

In this issue of the Journal, Wyss et al. (Am J Epidemiol. 2016;184(10):703-716) describe the association between use of smokeless tobacco and head and neck cancer in 11 US case-control studies. Despite use by an estimated 300 million people worldwide and prior evidence for a causal association with cancer, these products remain understudied. Data are particularly needed for persons who do not use cigarettes or other smoking tobacco products. With 6,772 cancer cases and 8,375 controls, the current study is larger than previous efforts, allowing evaluation of associations among never cigarette smokers. Importantly, snuff use was positively associated with head and neck cancer, particularly for cancers of the oral cavity, whereas associations were weaker for chewing tobacco. Associations were observed among never cigarette smokers but not among ever cigarette smokers. Yet, despite the large sample size, only 44 cases and 62 controls had used snuff and only 61 cases and 96 controls had used chewing tobacco in the absence of cigarettes, precluding detailed examinations of dose response and cessation. Future studies set in high-prevalence populations with detailed assessment of lifetime use are needed to better understand the cancer risks of exclusive smokeless tobacco use and dual use of smokeless tobacco with other tobacco products, including cigarettes.