Invited Commentary: Smokeless Tobacco—An Important Contributor to Cancer, but More Work Is Needed
Am J Epidemiol.
Invited Commentary: Smokeless Tobacco-An Important Contributor to Cancer 0
but More Work Is Needed 0
Neal D. Freedman ) 0
0 Medical Center Way , MSC 9768, Rockville, MD 20850 (
American Journal of Epidemiology © Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health 2016. This work is written by (a) US Government employee(s) and is in the public domain in the US. 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. case-control studies; cigarettes; head and neck neoplasms; smokeless tobacco Abbreviations: CI, confidence interval; OR, odds ratio.
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An estimated 300 million people worldwide use
smokeless tobacco products (1), with nearly 90% of use occurring
in Southeast Asia. In the United States, approximately
2.6% of adults (4.8% of men and 0.3% of women) currently
use smokeless tobacco products (2). However, substantial
geographic variation is observed, with the prevalence of
current use ranging from 1.5% in the District of Columbia and
Massachusetts to 9.4% in West Virginia (3). Whereas the
adult prevalence of cigarette smoking has declined in the
United States over time (4), the prevalence of smokeless
tobacco use among US adults has been largely stable over
the last 10 years (5). Smokeless tobacco use is also common
among youth, with recent data indicating that 9.9% of male
high school students and 1.2% of female high school
students had used it in the past 30 days, compared with 10.6%
of male students and 7.9% of female students who smoked
cigarettes (6).
Smokeless tobacco contains nicotine as well more than
30 carcinogens, such as tobacco-specific nitrosamines and
polycyclic aromatic hydrocarbons (1, 7). The International
Agency for Research on Cancer has determined that
smokeless tobacco products are carcinogenic to humans and that
such products are causally related to cancers of the oral
cavity, esophagus, and pancreas (8). Nevertheless, far less
information is available on the health effects of smokeless
tobacco than is available for cigarette smoking. Perhaps the
greatest amount of data is available for cancers of the oral
cavity and overall head and neck. Yet even here, there are
many remaining research questions. Smokeless tobacco
products also differ substantially around the world, varying
in chemical composition and in the way that they are used
(1), necessitating a range of studies that carefully assess
associations with different types of tobacco products. Within
the United States and elsewhere, previous studies have
often been limited by small sample sizes and have lacked
comprehensive assessment of lifetime use patterns. Many
smokeless tobacco users in these studies also used
cigarettes, which has made it challenging to define the risks of
exclusive smokeless tobacco use.
Within this context, the paper by Wyss et al. (9) in this
issue of the Journal provides important information on
the association of smokeless tobacco products with head
and neck cancer. The study is set within the International
Head and Neck Cancer Epidemiology Consortium and
includes data from 11 US case-control studies, representing
6,772 cancer cases and 8,375 controls. The large sample
size of this study provides numerous advantages,
including the possibility of investigating associations among
never cigarette smokers and within subsites of head and
neck cancer. Importantly, among never cigarette smokers,
ever users of snuff had higher risks of head and neck
cancer (odds ratio (OR) = 1.71, 95% confidence
interval (CI): 1.08, 2.70), particularly for oral cavity cancer
(OR = 3.01, 95% CI: 1.63, 5.55) (9). Associations for
ever use of chewing tobacco among (...truncated)